[COOK-2676]: fix rabbitmq-server restarts when using clustering

https://tickets.opscode.com/browse/COOK-2676

On ubuntu with rabbitmq 2.7.x the safest way to get clustering to work is to stop rabbitmq, lay down the erlang cookie, remove /var/lib/rabbitmq/mnesia, and then restart rabbitmq.

This pull request also adds a sleep to the stop of rabbitmq-server so we can more accurately stop it if rabbitmq isn't up and ready for a stop command to be issued.

This code block is only run if the erlang cookie doesn't match the one that we expect so it is safe