HDFS-4542. Webhdfs doesn't support secure proxy users. Contributed by Daryn Sharp.

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HDFS-4553. Webhdfs will NPE on some unexpected response codes. Contributed by Daryn Sharp.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1452994 13f79535-47bb-0310-9956-ffa450edef68