svn merge -c 1487498 FIXES: YARN-512. Log aggregation root directory check is more expensive than it needs to be. Contributed by Maysam Yabandeh


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1487500 13f79535-47bb-0310-9956-ffa450edef68