RabbitMQ Receiver - delay mechanism when send fails

[KristianLyng]

This will build upon #259

The idea is to use RabbitMQ as a means to queue data when the regular storage path is unavailable. On the sender, we can solve this with the fallback sender, however, just reading continuously will just spam both skogul, rabbitmq and the struggling storage engine.

So we need SOME sort of mechanism to report whether or not to send data.

This issue is to somehow address this. Unknown how.

[KristianLyng]

An obvious method is to combine this with backoff-sender, but limit how many fetches we do from the MQ.