'Make a remote process call to retrieve the external network id.
@raise oslo_messaging.RemoteError: with TooManyExternalNetworks as
exc_type if there are more than one
external network'

def get_external_network_id(self, context):

    cctxt = self.client.prepare()
    return cctxt.call(context, 'get_external_network_id', host=self.host)
