Adding support for EL and rabbitmq_clustering

I have refactored things a bit, so that I could consume your role from a RH/Centos box.
Also added clustering support, so that a vagrant up, will provision two boxes and add the '2nd,3rd...' boxes to join the cluster with the first box.

'works on my machine'
One drawback to this method, it doesn't enable clustering post reboot.  You will need to login and re-configure.