Merge r1526332 from branch-2 to branch-2.1-beta 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-2.1-beta@1526333 13f79535-47bb-0310-9956-ffa450edef68