YARN-1157. Fixed ResourceManager UI to behave correctly when apps like distributed-shell do not set tracking urls. Contributed by Xuan Gong.
svn merge --ignore-ancestry -c 1526371 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1526374 13f79535-47bb-0310-9956-ffa450edef68