HBASE-5930. Added unit tests and configuration value for disabling the automatic flush

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1482161 13f79535-47bb-0310-9956-ffa450edef68
HBASE-8527 clean up code around compaction completion in HStore

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1482164 13f79535-47bb-0310-9956-ffa450edef68