Merge r1583203 from trunk. YARN-1893. Mark AtMostOnce annotation to ApplicationMasterProtocol#allocate. Contributed by Xuan Gong

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1583205 13f79535-47bb-0310-9956-ffa450edef68