Merge -c from trunk to branch-2 to fix YARN-701. Use application tokens irrespective of secure or non-secure mode. Contributed by Vinod K V.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1504605 13f79535-47bb-0310-9956-ffa450edef68
svn merge -c 1504645 FIXES: MAPREDUCE-5265. History server admin service to refresh user and superuser group mappings. Contributed by Ashwin Shankar


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1504653 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-2' into branch-2-gd
Merge remote branch 'origin/branch-2-gd' into fb-HADOOP-7435-branch-2-gd