loadbalancer: implement rabbitmq binding

Implement RabbitMQ binding with these options:
- disabled by default for backward compatibility
- '5672' is the port by default
- mode TCP with roundrobin balance
messaging: support HAproxy binding

As an option and disabled by default for backward compatibility, allow
to export a puppet resource to create HAproxy binding for RabbitMQ
service.
Also add an option to specify the RabbitMQ service TCP port.
Merge pull request #652 from enovance/rabbit-haproxy

RabbitMQ load-balancing support