KAFKA-1327 Add log cleaner metrics.
KAFKA-1356; follow-up - return unknown topic partition on non-existent
topic if auto.create is off; reviewed by Timothy Chen, Neha Narkhede and
Jun Rao.
KAFKA-1327; Log cleaner metrics follow-up patch to reset dirtiest log
cleanable ratio; reviewed by Jun Rao
Merge branch '0.8.1' of https://git-wip-us.apache.org/repos/asf/kafka into 0.8.1-stbx