Pick up fixes to GAPIC generator. (googleapis#6513)

Closes googleapis#6498.

Includes fixes from these PRs:

- googleapis/gapic-generator#2407
- googleapis/gapic-generator#2396.

iot/google/cloud/iot_v1/gapic/device_manager_client.py

@@ -112,7 +112,7 @@ def __init__(self,
                  transport=None,
                  channel=None,
                  credentials=None,
-                 client_config=device_manager_client_config.config,
+                 client_config=None,
                  client_info=None):
         """Constructor.
 
@@ -145,13 +145,20 @@ def __init__(self,
                 your own client library.
         """
         # Raise deprecation warnings for things we want to go away.
-        if client_config:
-            warnings.warn('The `client_config` argument is deprecated.',
-                          PendingDeprecationWarning)
+        if client_config is not None:
+            warnings.warn(
+                'The `client_config` argument is deprecated.',
+                PendingDeprecationWarning,
+                stacklevel=2)
+        else:
+            client_config = device_manager_client_config.config
+
         if channel:
             warnings.warn(
                 'The `channel` argument is deprecated; use '
-                '`transport` instead.', PendingDeprecationWarning)
+                '`transport` instead.',
+                PendingDeprecationWarning,
+                stacklevel=2)
 
         # Instantiate the transport.
         # The transport is responsible for handling serialization and

iot/google/cloud/iot_v1/gapic/transports/device_manager_grpc_transport.py

@@ -65,6 +65,8 @@ def __init__(self,
                 credentials=credentials,
             )
 
+        self._channel = channel
+
         # gRPC uses objects called "stubs" that are bound to the
         # channel and provide a basic method for each RPC.
         self._stubs = {
@@ -95,6 +97,15 @@ def create_channel(cls,
             scopes=cls._OAUTH_SCOPES,
         )
 
+    @property
+    def channel(self):
+        """The gRPC channel used by the transport.
+
+        Returns:
+            grpc.Channel: A gRPC channel object.
+        """
+        return self._channel
+
     @property
     def create_device_registry(self):
         """Return the gRPC stub for {$apiMethod.name}.

iot/synth.py

@@ -29,3 +29,5 @@
     artman_output_name='iot-v1')
 
 s.move(library / 'google/cloud/iot_v1')
+s.move(library / 'tests/unit/gapic')
+s.move(library / 'tests/system/gapic')

iot/tests/system/gapic/v1/test_system_device_manager_v1.py

@@ -1,3 +1,5 @@
+# -*- coding: utf-8 -*-
+#
 # Copyright 2018 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");