Adjust Spanner tests for grpcio 1.2.0 (googleapis#3178)

Author: lukesneeringer

spanner/setup.py

@@ -51,7 +51,7 @@
 
 REQUIREMENTS = [
     'google-cloud-core >= 0.23.1, < 0.24dev',
-    'grpcio >= 1.0.2, < 2.0dev',
+    'grpcio >= 1.2.0, < 2.0dev',
     'gapic-google-cloud-spanner-v1 >= 0.15.0, < 0.16dev',
     'gapic-google-cloud-spanner-admin-database-v1 >= 0.15.0, < 0.16dev',
     'gapic-google-cloud-spanner-admin-instance-v1 >= 0.15.0, < 0.16dev',

spanner/unit_tests/test_session.py

@@ -847,15 +847,15 @@ def begin_transaction(self, session, options_, options=None):
     def _trailing_metadata(self):
         from google.protobuf.duration_pb2 import Duration
         from google.rpc.error_details_pb2 import RetryInfo
-        from grpc._common import cygrpc_metadata
+        from grpc._common import to_cygrpc_metadata
 
         if self._commit_abort_retry_nanos is None:
-            return cygrpc_metadata(())
+            return to_cygrpc_metadata(())
         retry_info = RetryInfo(
             retry_delay=Duration(
                 seconds=self._commit_abort_retry_seconds,
                 nanos=self._commit_abort_retry_nanos))
-        return cygrpc_metadata([
+        return to_cygrpc_metadata([
             ('google.rpc.retryinfo-bin', retry_info.SerializeToString())])
 
     def commit(self, session, mutations,