svn merge -c 1579396 from trunk for HDFS-6123. Do not log stack trace for ReplicaAlreadyExistsException and SocketTimeoutException.


git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2.4@1579398 13f79535-47bb-0310-9956-ffa450edef68