MB-5904: don't log bucket config that libvbucket didn't like

Because it may contain bucket's sasl password

Change-Id: I88e9d721179cee1b457a71de72dafc5a1c1c9df9
Reviewed-on: http://review.couchbase.org/28051
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Artem Stemkovski <artem@couchbase.com>