ClusterPortManager: fix zk watcher leak

getConfig gets called out of the port watcher, therefore it should
not set other such watchers. The activation watcher is now set
out of registerNewBuilder, removing the watcher leak.

Change-Id: I78c3870875c17c229f796286116b11d3ec37e540
Signed-off-by: Guillermo Ontanon <guillermo@midokura.jp>
Merge "ClusterPortManager: fix zk watcher leak"