YARN-2853. Merging to branch-2.6 for hadoop-2.6.0-rc1.

(cherry picked from commit d648e60ebab7f1942dba92e9cd2cb62b8d70419b)
YARN-2635. Merging to branch-2.6 for hadoop-2.6.0-rc1.

(cherry picked from commit 81dc0ac6dcf2f34ad607da815ea0144f178691a9)