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 _ in iter_queue(self.queues[queue_name]):
            self.queues[queue_name].task_done()