MB-100 prevent leaking of the private key to logs and diag

sanitization was not working when there is a vclock attached

Change-Id: Ifc10d59468ce5d699e749ae332bd299d9b87b971
Reviewed-on: http://review.couchbase.org/33058
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>