svn merge -c 1470660 from branch-1 for HDFS-4715. Backport HDFS-3577, HDFS-3318 and HDFS-3788: fix some WebHDFS performance issues.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-1.2@1470661 13f79535-47bb-0310-9956-ffa450edef68