fix default value for max segments to merge
fix minor link problem in docs
fail task on exception

If the task announcement throw exception, set status to fail instead of
retrying it again and again.
Merge pull request #573 from metamx/task-fail-on-exception

fail task on exception
clean up a bit of the logic in RTR failure with exceptions in announceTask
prepare for next release
remove druid-hll
[maven-release-plugin] prepare release druid-0.6.116
[maven-release-plugin] prepare for next development iteration