Get gerrit events from RabbitMQ as message queue service

This patch adds implementation of MessageQueueListener extension in
RabbitMQ Consumer Plugin.

https://wiki.jenkins-ci.org/display/JENKINS/RabbitMQ+Consumer+Plugin

Using this feature, we can trigger job by gerrit event in message queue.

At first, I had plan to release this as independent plugin. But after some study,
I concluded that it should be implemented to this plugin.

* Very simple code
* Optional flags to ignore NoClassDefException related to other plugins
  * No impact if those are not installed

So I would be glad if you merge this.