Merge 1529369 from trunk to branch-2 for YARN-1251. TestDistributedShell#TestDSShell failed with timeout. Contributed by Xuan Gong.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1529370 13f79535-47bb-0310-9956-ffa450edef68