YARN-1717. Enabled periodically discarding old data in LeveldbTimelineStore. Contributed by Billie Rinaldi.
svn merge --ignore-ancestry -c 1577693 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1577700 13f79535-47bb-0310-9956-ffa450edef68