• After issuing a stop stream assignment, the leader polls the zookeeper to confirm that tasks have stopped. Currently that poll happens in the main event thread.
• There is also a requirement that the coordinator should process all of its events in less than 30 seconds. If this requirement is not met the coordinator won't be able to punch heartbeats.
• If the coordinator is configured to wait for stop propagation for a prolonged time, it will block the event queue for more than 30 seconds.

This change fixes the problem by moving the task to wait for stop request to propagate to a separate thread.