HDFS-4835. Port trunk WebHDFS changes to branch-0.23. Contributed by Robert Parker.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1484574 13f79535-47bb-0310-9956-ffa450edef68
Merge remote branch 'origin/branch-0.23' into branch-0.23-gd
Merge remote branch 'origin/branch-0.23-gd' into fb-xxx-hadoop-auth-kerberos-realm-branch-0.23-gd