Create and return a gRPC channel object.

        Args:
            address (str): The host for the channel to use.
            credentials (~.Credentials): The
                authorization credentials to attach to requests. These
                credentials identify this application to the service. If
                none are specified, the client will attempt to ascertain
                the credentials from the environment.

        Returns:
            grpc.Channel: A gRPC channel object.

def create_channel(cls, address="spanner.googleapis.com:443", credentials=None):
        """Create and return a gRPC channel object.

        Args:
            address (str): The host for the channel to use.
            credentials (~.Credentials): The
                authorization credentials to attach to requests. These
                credentials identify this application to the service. If
                none are specified, the client will attempt to ascertain
                the credentials from the environment.

        Returns:
            grpc.Channel: A gRPC channel object.
        """
        grpc_gcp_config = grpc_gcp.api_config_from_text_pb(
            pkg_resources.resource_string(__name__, _SPANNER_GRPC_CONFIG)
        )
        options = [(grpc_gcp.API_CONFIG_CHANNEL_ARG, grpc_gcp_config)]
        return google.api_core.grpc_helpers.create_channel(
            address, credentials=credentials, scopes=cls._OAUTH_SCOPES
        )