HDFS-5400. DFS_CLIENT_MMAP_CACHE_THREAD_RUNS_PER_TIMEOUT constant is set to the wrong value (Colin Patrick McCabe)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1534656 13f79535-47bb-0310-9956-ffa450edef68