Tests: The rmq tests create exchanges and queues for that are not cleaned up

[sphuber]

The loop_communicator fixture creates these by instantiating a RmqCommunicator but does not delete them. It is not sure if this can even be done through the AMQP protocol. It might need to be done through the management HTTP API, or the communicator should be mocked to never actually even interact with RabbitMQ.