Consumer restart causes duplicate messages

[sobychacko]

Scenario:

1. Start an exclusive consumer--> Receive message.
2. Stop the consumer.
3. Restart the consumer or start another consumer under the same subscription name.
4. Occasionally, the same message that was already seen by the first consumer reappears in the second consumer.

The reason is because in step 2 above, when we stop the container if there are any acks in progress, they are immediately aborted by stopping the consumer and then the container is stopped. We need to wait for the consumer thread to finish what it is doing before stopping the consumer.