Merge r1499886 from trunk to branch-2. YARN-845. RM crash with NPE on NODE_UPDATE (bikas)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1499888 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd