MB-11724 announce config changes during the config upgrade

...so they get replicated to the other nodes quickly

Change-Id: I3ac33ffa087401ea285da07c739054e8de2d4454
Reviewed-on: http://review.couchbase.org/39706
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>