P2P: Better error when status not found

[heifner]

$ cleos -u http://localhost:8889 net status foo
Error 3200005: http request fail
Error Details:
Error code 201
: null

This is because status implemented as:

   std::optional<connection_status> connections_manager::status( const string& host )const {
      connection_ptr con;
      {
         std::shared_lock g( connections_mtx );
         con = find_connection_i( host );
      }
      if( con ) {
         return con->get_status();
      }
      return {};
   }