Merge -r 1428313:1428314 from trunk to branch-2. Fixes: YARN-192. Node update causes NPE in the fair scheduler. Contributed by Sandy Ryza

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1428316 13f79535-47bb-0310-9956-ffa450edef68