HADOOP-10448. Support pluggable mechanism to specify proxy user settings (Contributed by Benoy Antony)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1598396 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6461. Use Time#monotonicNow to compute duration in DataNode#shutDown. Contributed by James Thomas.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1598399 13f79535-47bb-0310-9956-ffa450edef68