Improve client queue handling at shutdown.
Improve client queue handling at shutdown.

 - Don't ack requeued messages (missing return seems like it was a bug).
 - More logging around this event.

galaxyproject/pulsar,natefoo/pulsar,jmchilton/pulsar,ssorgatem/pulsar,ssorgatem/pulsar,natefoo/pulsar,jmchilton/pulsar,galaxyproject/pulsar