svn merge -c 1536711 FIXES: MAPREDUCE-5596. Allow configuring the number of threads used to serve shuffle connections. Contributed by Sandy Ryza


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.2@1536722 13f79535-47bb-0310-9956-ffa450edef68