HADOOP-10566. Refactor proxyservers out of ProxyUsers. (Contributed by Benoy Antony)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1598140 13f79535-47bb-0310-9956-ffa450edef68
HDFS-6453. Use Time#monotonicNow to avoid system clock reset. Contributed by Liang Xie.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1598145 13f79535-47bb-0310-9956-ffa450edef68