HDFS-5246. Merging change r1526316 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1526319 13f79535-47bb-0310-9956-ffa450edef68
Merge r1526330 from trunk to branch-2 for YARN-49. Improve distributed shell application to work on a secure cluster. Contributed by Vinod Kumar Vavilapalli.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1526332 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5503. Fixed a test issue in TestMRJobClient. Contributed by Jian He.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1526364 13f79535-47bb-0310-9956-ffa450edef68