Handle absence of repl_type in bucket config during upr upgrade.

Change-Id: I5a388096c89ac10230b128c7eba563aaa3363571
Reviewed-on: http://review.couchbase.org/36155
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>