Merge r1550579 from trunk to branch-2 to fix YARN-1311. Fixed app specific scheduler-events' names to be app-attempt based. Contributed by Vinod Kumar Vavilapalli

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1550584 13f79535-47bb-0310-9956-ffa450edef68