Implement openstacklib::messaging::rabbitmq

* Add puppetlabs-rabbitmq 4.x as a dependency in fixtures &
  metadata.json
* Implement openstacklib::messaging::rabbitmq to manage user, permissions
  and vhost in RabbitMQ (+ unit tests)
* Documentation

Change-Id: I65190035b51f3d72e4302dae7fad92a280d63cff