tests: Call real consume method of queue processors.

This switches to more real tests for a first batch of
queue_json_publish() calls that don't cause trouble when
used with call_consume_tests=True.

zerver/worker/queue_processors.py

@@ -393,6 +393,8 @@ class MessageSenderWorker(QueueProcessingWorker):
         self.redis_client.hmset(redis_key, {'status': 'complete',
                                             'response': resp_content})
 
+        # Since this sends back to Tornado, we can't use
+        # call_consume_in_tests here.
         queue_json_publish(server_meta['return_queue'], result, lambda e: None)
 
 @assign_queue('digest_emails')