YARN-981. Fixed YARN webapp so that /logs servlet works like before. Contributed by Jian He.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1519213 13f79535-47bb-0310-9956-ffa450edef68
HDFS-5136. Merging change r1519229 from branch-2

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1519231 13f79535-47bb-0310-9956-ffa450edef68