Add cluster support for rabbitmq element

Nodes can be joined into rabbitmq cluster now. This
patch sets up firewall, makes sure that hostname translation works
for rabbitmq nodes and automates adding nodes into cluster. See
rabbitmq-server/README for more details.

Change-Id: Idfb0a168fd2fd19b8fca4fa410c79091b636d79b
Merge "Add cluster support for rabbitmq element"