Refactor heartbeat generationto reduce duplication.

mechanism for connecting to rabbitMQ etc.  This refactors the heartbeat
generation to use the existing queue_publisher.
Make heartbeat integration tests invoke rake task.

To ensure they are a full end-to-end test
Include message options in errbit error report
Merge pull request #87 from alphagov/heartbeat_sending_refactor

Refactor heartbeat generation to reduce duplication.