YARN-1435. Modified Distributed Shell to accept either the command or the custom script. Contributed by Xuan Gong.
svn merge --ignore-ancestry -c 1550867 ../../trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1550869 13f79535-47bb-0310-9956-ffa450edef68