svn merge -c 1511823 from trunk to branch-2.1.0-beta to FIX HADOOP-9850. RPC kerberos errors don't trigger relogin.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.1.0-beta@1511827 13f79535-47bb-0310-9956-ffa450edef68