Log vclocks together with config changes.

Change-Id: Id88909d7aa2b788024da581a5bc43fce78c4b4d5
Reviewed-on: http://review.couchbase.org/37133
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>