ZOOKEEPER-1796. Move common code from {Follower, Observer}ZooKeeperServer into LearnerZooKeeperServer (Raul Gutierrez Segales via michim)


git-svn-id: https://svn.apache.org/repos/asf/zookeeper/trunk@1579888 13f79535-47bb-0310-9956-ffa450edef68