HDFS-6722. Display readable last contact time for dead nodes on NN webUI. Contributed by Ming Ma.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1616669 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-10771. Refactor HTTP delegation support out of httpfs to common, PART 1. (tucu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1616671 13f79535-47bb-0310-9956-ffa450edef68
HADOOP-10771. Refactor HTTP delegation support out of httpfs to common, PART 2. (tucu)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1616672 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6772. Get DN storages out of blockContentsStale state faster after NN restarts. (Contributed by Ming Ma)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1616680 13f79535-47bb-0310-9956-ffa450edef68