Drop all the messages from a queue.

        Parameters:
          queue_name(str): The queue to flush.

def flush(self, queue_name):
        """Drop all the messages from a queue.

        Parameters:
          queue_name(str): The queue to flush.
        """
        for name in (queue_name, dq_name(queue_name), xq_name(queue_name)):
            self.channel.queue_purge(name)