HDFS-5213. TestDataNodeConfig failing on Jenkins runs due to DN web port in use. (wang)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1589477 13f79535-47bb-0310-9956-ffa450edef68
Merge HADOOP-10251. Both NameNodes could be in STANDBY State if SNN network is unstable. Contributed by Vinayakumar B.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1589495 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6274. Merge r1589506 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1589507 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6275. Merge r1589510 from trunk.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1589511 13f79535-47bb-0310-9956-ffa450edef68