HDFS-6462. Merging change r1598405 from trunk

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1598407 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6356. Merged from r1598408. Fix typo in DatanodeLayoutVersion. Contributed by Tulasi G.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1598409 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6447. balancer should timestamp the completion message. Contributed by Juan Yu.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1598412 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-10639. FileBasedKeyStoresFactory initialization is not using default for SSL_REQUIRE_CLIENT_CERT_KEY. (tucu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1598415 13f79535-47bb-0310-9956-ffa450edef68