HDFS-4367. GetDataEncryptionKeyResponseProto does not handle null response. Contributed by Suresh Srinivas.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1431459 13f79535-47bb-0310-9956-ffa450edef68
MAPREDUCE-4907. Ammendment, forgot to svn add testcase in original commit

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1431510 13f79535-47bb-0310-9956-ffa450edef68