Preparing for release 4.3.0

git-svn-id: https://svn.apache.org/repos/asf/zookeeper/bookkeeper/trunk@1629124 13f79535-47bb-0310-9956-ffa450edef68
Bump version number to 4.4.0

git-svn-id: https://svn.apache.org/repos/asf/zookeeper/bookkeeper/trunk@1629127 13f79535-47bb-0310-9956-ffa450edef68