Merge r1506752 from branch-2 to branch-2.1-beta for YARN-875. Application can hang if AMRMClientAsync callback thread has exception (Xuan Gong via bikas)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1506755 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-5213. Re-assess TokenCache methods marked @Private. (kkambatl via tucu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1506761 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-9701. mvn site ambiguous links in hadoop-common. (kkambatl via tucu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1-beta@1506766 13f79535-47bb-0310-9956-ffa450edef68