Don't hardcode int64_t for duration type representations

In LLVM's `libcxx`, `int64_t` doesn't match chrono literals. See example below. To compile, run  `clang++-6.0 -stdlib=libc++ -std=c++14 TEST.cpp`

TEST.cpp
```
using namespace std::chrono_literals;

template<typename RatioT = std::milli>
bool
wait_for_service(
   std::chrono::duration<int64_t, RatioT> timeout
)
{
   return timeout == std::chrono::nanoseconds(0);
}

int main() {
   wait_for_service(2s);
   return 0;
}

```

Result of compilation
```
TEST.cpp:14:4: error: no matching function for call to 'wait_for_service'
   wait_for_service(2s);
   ^~~~~~~~~~~~~~~~
TEST.cpp:6:1: note: candidate template ignored: could not match 'long' against 'long long'
wait_for_service(
^
1 error generated.
```

rclcpp/include/rclcpp/client.hpp

@@ -78,10 +78,10 @@ class ClientBase
   bool
   service_is_ready() const;
 
-  template<typename RatioT = std::milli>
+  template<typename RepT = int64_t, typename RatioT = std::milli>
   bool
   wait_for_service(
-    std::chrono::duration<int64_t, RatioT> timeout = std::chrono::duration<int64_t, RatioT>(-1))
+    std::chrono::duration<RepT, RatioT> timeout = std::chrono::duration<RepT, RatioT>(-1))
   {
     return wait_for_service_nanoseconds(
       std::chrono::duration_cast<std::chrono::nanoseconds>(timeout)

rclcpp/include/rclcpp/executor.hpp

@@ -151,11 +151,11 @@ class Executor
    * spin_node_once to block indefinitely (the default behavior). A timeout of 0 causes this
    * function to be non-blocking.
    */
-  template<typename T = std::milli>
+  template<typename RepT = int64_t, typename T = std::milli>
   void
   spin_node_once(
     rclcpp::node_interfaces::NodeBaseInterface::SharedPtr node,
-    std::chrono::duration<int64_t, T> timeout = std::chrono::duration<int64_t, T>(-1))
+    std::chrono::duration<RepT, T> timeout = std::chrono::duration<RepT, T>(-1))
   {
     return spin_node_once_nanoseconds(
       node,
@@ -164,11 +164,11 @@ class Executor
   }
 
   /// Convenience function which takes Node and forwards NodeBaseInterface.
-  template<typename NodeT = rclcpp::Node, typename T = std::milli>
+  template<typename NodeT = rclcpp::Node, typename RepT = int64_t, typename T = std::milli>
   void
   spin_node_once(
     std::shared_ptr<NodeT> node,
-    std::chrono::duration<int64_t, T> timeout = std::chrono::duration<int64_t, T>(-1))
+    std::chrono::duration<RepT, T> timeout = std::chrono::duration<RepT, T>(-1))
   {
     return spin_node_once_nanoseconds(
       node->get_node_base_interface(),
@@ -218,11 +218,11 @@ class Executor
    *   code.
    * \return The return code, one of `SUCCESS`, `INTERRUPTED`, or `TIMEOUT`.
    */
-  template<typename ResponseT, typename TimeT = std::milli>
+  template<typename ResponseT, typename TimeRepT = int64_t, typename TimeT = std::milli>
   FutureReturnCode
   spin_until_future_complete(
     std::shared_future<ResponseT> & future,
-    std::chrono::duration<int64_t, TimeT> timeout = std::chrono::duration<int64_t, TimeT>(-1))
+    std::chrono::duration<TimeRepT, TimeT> timeout = std::chrono::duration<TimeRepT, TimeT>(-1))
   {
     // TODO(wjwwood): does not work recursively; can't call spin_node_until_future_complete
     // inside a callback executed by an executor.

rclcpp/include/rclcpp/executors.hpp

@@ -65,13 +65,13 @@ using rclcpp::executors::SingleThreadedExecutor;
  *   If the time spent inside the blocking loop exceeds this timeout, return a `TIMEOUT` return code.
  * \return The return code, one of `SUCCESS`, `INTERRUPTED`, or `TIMEOUT`.
  */
-template<typename ResponseT, typename TimeT = std::milli>
+template<typename ResponseT, typename TimeRepT = int64_t, typename TimeT = std::milli>
 rclcpp::executor::FutureReturnCode
 spin_node_until_future_complete(
   rclcpp::executor::Executor & executor,
   rclcpp::node_interfaces::NodeBaseInterface::SharedPtr node_ptr,
   std::shared_future<ResponseT> & future,
-  std::chrono::duration<int64_t, TimeT> timeout = std::chrono::duration<int64_t, TimeT>(-1))
+  std::chrono::duration<TimeRepT, TimeT> timeout = std::chrono::duration<TimeRepT, TimeT>(-1))
 {
   // TODO(wjwwood): does not work recursively; can't call spin_node_until_future_complete
   // inside a callback executed by an executor.
@@ -81,13 +81,13 @@ spin_node_until_future_complete(
   return retcode;
 }
 
-template<typename NodeT = rclcpp::Node, typename ResponseT, typename TimeT = std::milli>
+template<typename NodeT = rclcpp::Node, typename ResponseT, typename TimeRepT = int64_t, typename TimeT = std::milli>
 rclcpp::executor::FutureReturnCode
 spin_node_until_future_complete(
   rclcpp::executor::Executor & executor,
   std::shared_ptr<NodeT> node_ptr,
   std::shared_future<ResponseT> & future,
-  std::chrono::duration<int64_t, TimeT> timeout = std::chrono::duration<int64_t, TimeT>(-1))
+  std::chrono::duration<TimeRepT, TimeT> timeout = std::chrono::duration<TimeRepT, TimeT>(-1))
 {
   return rclcpp::executors::spin_node_until_future_complete(
     executor,
@@ -98,23 +98,23 @@ spin_node_until_future_complete(
 
 }  // namespace executors
 
-template<typename FutureT, typename TimeT = std::milli>
+template<typename FutureT, typename TimeRepT = int64_t, typename TimeT = std::milli>
 rclcpp::executor::FutureReturnCode
 spin_until_future_complete(
   rclcpp::node_interfaces::NodeBaseInterface::SharedPtr node_ptr,
   std::shared_future<FutureT> & future,
-  std::chrono::duration<int64_t, TimeT> timeout = std::chrono::duration<int64_t, TimeT>(-1))
+  std::chrono::duration<TimeRepT, TimeT> timeout = std::chrono::duration<TimeRepT, TimeT>(-1))
 {
   rclcpp::executors::SingleThreadedExecutor executor;
   return executors::spin_node_until_future_complete<FutureT>(executor, node_ptr, future, timeout);
 }
 
-template<typename NodeT = rclcpp::Node, typename FutureT, typename TimeT = std::milli>
+template<typename NodeT = rclcpp::Node, typename FutureT, typename TimeRepT = int64_t, typename TimeT = std::milli>
 rclcpp::executor::FutureReturnCode
 spin_until_future_complete(
   std::shared_ptr<NodeT> node_ptr,
   std::shared_future<FutureT> & future,
-  std::chrono::duration<int64_t, TimeT> timeout = std::chrono::duration<int64_t, TimeT>(-1))
+  std::chrono::duration<TimeRepT, TimeT> timeout = std::chrono::duration<TimeRepT, TimeT>(-1))
 {
   return rclcpp::spin_until_future_complete(node_ptr->get_node_base_interface(), future, timeout);
 }

rclcpp/include/rclcpp/node.hpp

@@ -234,10 +234,10 @@ class Node : public std::enable_shared_from_this<Node>
    * \param[in] callback User-defined callback function.
    * \param[in] group Callback group to execute this timer's callback in.
    */
-  template<typename DurationT = std::milli, typename CallbackT>
+  template<typename DurationRepT = int64_t, typename DurationT = std::milli, typename CallbackT>
   typename rclcpp::WallTimer<CallbackT>::SharedPtr
   create_wall_timer(
-    std::chrono::duration<int64_t, DurationT> period,
+    std::chrono::duration<DurationRepT, DurationT> period,
     CallbackT callback,
     rclcpp::callback_group::CallbackGroup::SharedPtr group = nullptr);
 

rclcpp/include/rclcpp/node_impl.hpp

@@ -165,10 +165,10 @@ Node::create_subscription(
     allocator);
 }
 
-template<typename DurationT, typename CallbackT>
+template<typename DurationRepT, typename DurationT, typename CallbackT>
 typename rclcpp::WallTimer<CallbackT>::SharedPtr
 Node::create_wall_timer(
-  std::chrono::duration<int64_t, DurationT> period,
+  std::chrono::duration<DurationRepT, DurationT> period,
   CallbackT callback,
   rclcpp::callback_group::CallbackGroup::SharedPtr group)
 {

rclcpp/include/rclcpp/parameter_client.hpp

@@ -138,10 +138,10 @@ class AsyncParametersClient
   bool
   service_is_ready() const;
 
-  template<typename RatioT = std::milli>
+  template<typename RepT = int64_t, typename RatioT = std::milli>
   bool
   wait_for_service(
-    std::chrono::duration<int64_t, RatioT> timeout = std::chrono::duration<int64_t, RatioT>(-1))
+    std::chrono::duration<RepT, RatioT> timeout = std::chrono::duration<RepT, RatioT>(-1))
   {
     return wait_for_service_nanoseconds(
       std::chrono::duration_cast<std::chrono::nanoseconds>(timeout)
@@ -281,10 +281,10 @@ class SyncParametersClient
     return async_parameters_client_->service_is_ready();
   }
 
-  template<typename RatioT = std::milli>
+  template<typename RepT = int64_t, typename RatioT = std::milli>
   bool
   wait_for_service(
-    std::chrono::duration<int64_t, RatioT> timeout = std::chrono::duration<int64_t, RatioT>(-1))
+    std::chrono::duration<RepT, RatioT> timeout = std::chrono::duration<RepT, RatioT>(-1))
   {
     return async_parameters_client_->wait_for_service(timeout);
   }

rclcpp_action/include/rclcpp_action/client.hpp

@@ -66,10 +66,10 @@ class ClientBase : public rclcpp::Waitable
   action_server_is_ready() const;
 
   /// Wait for action_server_is_ready() to become true, or until the given timeout is reached.
-  template<typename RatioT = std::milli>
+  template<typename RepT = int64_t, typename RatioT = std::milli>
   bool
   wait_for_action_server(
-    std::chrono::duration<int64_t, RatioT> timeout = std::chrono::duration<int64_t, RatioT>(-1))
+    std::chrono::duration<RepT, RatioT> timeout = std::chrono::duration<RepT, RatioT>(-1))
   {
     return wait_for_action_server_nanoseconds(
       std::chrono::duration_cast<std::chrono::nanoseconds>(timeout)

rclcpp_lifecycle/include/rclcpp_lifecycle/lifecycle_node.hpp

@@ -222,10 +222,10 @@ class LifecycleNode : public node_interfaces::LifecycleNodeInterface,
    * \param[in] callback User-defined callback function.
    * \param[in] group Callback group to execute this timer's callback in.
    */
-  template<typename DurationT = std::milli, typename CallbackT>
+  template<typename DurationRepT = int64_t, typename DurationT = std::milli, typename CallbackT>
   typename rclcpp::WallTimer<CallbackT>::SharedPtr
   create_wall_timer(
-    std::chrono::duration<int64_t, DurationT> period,
+    std::chrono::duration<DurationRepT, DurationT> period,
     CallbackT callback,
     rclcpp::callback_group::CallbackGroup::SharedPtr group = nullptr);
 

rclcpp_lifecycle/include/rclcpp_lifecycle/lifecycle_node_impl.hpp

@@ -132,10 +132,10 @@ LifecycleNode::create_subscription(
     allocator);
 }
 
-template<typename DurationT, typename CallbackT>
+template<typename DurationRepT, typename DurationT, typename CallbackT>
 typename rclcpp::WallTimer<CallbackT>::SharedPtr
 LifecycleNode::create_wall_timer(
-  std::chrono::duration<int64_t, DurationT> period,
+  std::chrono::duration<DurationRepT, DurationT> period,
   CallbackT callback,
   rclcpp::callback_group::CallbackGroup::SharedPtr group)
 {