Add reference to channel in Client

Author: remingtonc

src/cisco_gnmi/client.py

@@ -99,6 +99,7 @@ def __init__(self, grpc_channel, timeout=_C_MAX_LONG):
             Timeout for gRPC functionality.
         """
         self.service = proto.gnmi_pb2_grpc.gNMIStub(grpc_channel)
+        self._channel = grpc_channel
 
     def capabilities(self):
         """Capabilities allows the client to retrieve the set of capabilities that