HDFS-4353. Encapsulate connections to peers in Peer and PeerServer classes. Contributed by Colin Patrick McCabe.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-347@1431097 13f79535-47bb-0310-9956-ffa450edef68
HDFS-4354. Create DomainSocket and DomainPeer and associated unit tests. Contributed by Colin Patrick McCabe.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/HDFS-347@1431102 13f79535-47bb-0310-9956-ffa450edef68