merge -c 1437245 from trunk to branch-2 to fix YARN-231. RM Restart - Add FS-based persistent store implementation for RMStateStore. Contributed by Bikas Saha

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1437246 13f79535-47bb-0310-9956-ffa450edef68
Merge branch 'branch-2' of github.com:griddynamics/yhadoop-common into branch-2-gd
Merge branch 'branch-2-gd' of github.com:griddynamics/yhadoop-common into fb-HADOOP-7435-branch-2-gd