Make 'snf-ganeti-eventd' daemon to send heartbeat messages which can
be used to check that the daemon is working correctly, i.e. that it is watching
the Ganeti queue and that it can send messages to the AMQP broker. The
daemon is triggered to send a heartbeat message by setting a special tag
to the Ganeti cluster in 'dry-run' mode.

Heartbeat messages are send with the 'eventd.heartbeat' routing key.

Refs Issue #23