Add ability to check if specified passwords match RabbitMQ DB and change if required

Renames the exec statement for fetching gpg key to be more descriptive.
Checks to make specified user passwords match configured passwords in RabbitMQ and resets if needed.
rabbitmq doesn't seem to have their own yum repo for this http://www.rabbitmq.com/install-rpm.html

I would prefer you didn't change this line since it's not relevant to the rest of the pull request.