merge -c r1460846 from trunk to branch-2 for YARN-497. Yarn unmanaged-am launcher jar does not define a main class in its manifest (Hitesh Shah via bikas)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1460847 13f79535-47bb-0310-9956-ffa450edef68