merge -c r1459555 from trunk to branch-2 for YARN-417. Create AMRMClient wrapper that provides asynchronous callbacks. (Sandy Ryza via bikas)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1459557 13f79535-47bb-0310-9956-ffa450edef68