Add support for Rabbitmq on Debian and admin option for ensure_user

Hello guys,

I'm sending this pull request and suggesting adding support for **RabbitMQ** on **Debian** distributions.

I'm working on a project for a standalone appliance based on Ubuntu and 12:04 (with these changes) could accrue RabbitMQ successfully!

Leveraging also includes an option in **ensure_user** method to configure an **administrator** user. So you can access the RabbitMQ Management Plugin smoothly.

Hope it can help you too.