YARN-1590. Fixed ResourceManager, web-app proxy and MR JobHistoryServer to expand _HOST properly in their kerberos principles. Contributed by Mohammad Kamrul Islam.
svn merge --ignore-ancestry -c 1569537 ../../trunk/


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1569539 13f79535-47bb-0310-9956-ffa450edef68