Discover the current coordinator for the group.

        Returns:
            Future: resolves to the node id of the coordinator

def _send_group_coordinator_request(self):
        """Discover the current coordinator for the group.

        Returns:
            Future: resolves to the node id of the coordinator
        """
        node_id = self._client.least_loaded_node()
        if node_id is None:
            return Future().failure(Errors.NoBrokersAvailable())

        elif not self._client.ready(node_id, metadata_priority=False):
            e = Errors.NodeNotReadyError(node_id)
            return Future().failure(e)

        log.debug("Sending group coordinator request for group %s to broker %s",
                  self.group_id, node_id)
        request = GroupCoordinatorRequest[0](self.group_id)
        future = Future()
        _f = self._client.send(node_id, request)
        _f.add_callback(self._handle_group_coordinator_response, future)
        _f.add_errback(self._failed_request, node_id, request, future)
        return future