MB-100: actually make config upgrader work

Change-Id: If51fff197bd042f8accea9a2a06a1e6b5ed31e92
Reviewed-on: http://review.couchbase.org/29944
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>