YARN-1595. Made enabling history service configurable and fixed test failures on branch YARN-321. Contributed by Vinod Kumar Vavilapalli.
svn merge --ignore-ancestry -c 1559001 ../YARN-321


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1562218 13f79535-47bb-0310-9956-ffa450edef68