Merge 1529370 from branch-2 to branch-2.1-beta 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-2.1-beta@1529371 13f79535-47bb-0310-9956-ffa450edef68