YARN-2288. Made persisted data in LevelDB timeline store be versioned. Contributed by Junping Du.
svn merge --ignore-ancestry -c 1616540 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1616541 13f79535-47bb-0310-9956-ffa450edef68