Prevent to requeue main task (run same main task in parallel).

If worker have problem with AMQP connection it can sometimes
do not get acknowledgements for message(main task) instantly
and if worker disconect at this time, message will be requeued
and we get several working tasks running in parallel.

Change-Id: If038079e263feb811d019d08944ff1dacd11f30a
Closes-Bug: #1340704