MB-39163: Avoid deadlock in leader if changech is full
MB-39163: Avoid deadlock in leader if changech is full

removeListener and AddFollower functions will notify on
the change channel while holding a lock. This can to a
deadlock if the changech is full. To avoid deadlock,
release the lock before notifying on the changech.

Change-Id: Ie93eb02621c42f60e351fbb66cdd7b26e77fceb6

couchbase/gometa