HADOOP-8943. Support multiple group mapping providers. Contributed by Kai Zheng

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1605857 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5939. StartTime showing up as the epoch time in JHS UI after upgrade. Contributed by Chen He


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1605892 13f79535-47bb-0310-9956-ffa450edef68