disable heartbeat in RabbitMQ server

reason: RabbitMQ 2.X did not use heartbeats by default, when RabbitMQ
3.X does. Pika's BlockingConnection does not send heartbeats, so the
connections to RabbitMQ are severed after three missed heartbeats
(3*10 min by default).

The quick way to fix this is to disable heartbeats, but a better way
would be to find how to make Pika send heartbeats.