Experiment with different topic_request_required_acks settings

Occasionally the kafka <-> zookeeper connection times out for broker analytics1021.
When this happens, we see some message loss, but varnishkafka reports that
all messages have been sent.  It is possible that analytics1021 is dropping messages
when it rejoins the ISR.

See Bug: 69667 for more information.

Change-Id: Id4deb19c4bfb720098109ba9e8e8f93020e0ad41