openstack-full: download last RabbitMQ release for Debian family

In Ubuntu LTS and Debian stable, RabbitMQ releases are to old to use
last clustering features (2.7).

This patch aims to download RabbitMQ > 3 from their APT repository.

Bug #40
Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>
Merge pull request #41 from enovance/enhancement/40/emilien

openstack-full: download last RabbitMQ release for Debian family