Whitespace
Add a service check to the RabbitMQ check based on aliveness.

Changes:
- Adds optional configuration to have a list of vhosts you want to
  monitor. The default case will fetch all vhosts from the API.
- Adds `rabbitmq.aliveness` check, tagged by vhost.
Clean-up rabbitmq check from review.
Merge pull request #1097 from DataDog/conor/rabbitmq-service-check

Add a service check to the RabbitMQ check based on aliveness.