MB-10116:bp: prevent leaking of the private key to logs and diag

sanitization was not working when there is a vclock attached

This is trivial cherry-pick.

Change-Id: I222b004d895852d9b9dea0560c2dc6367ec20a35
Orig-Reviewed-on: http://review.couchbase.org/33058
Signed-off-by: Aliaksey Kandratsenka <alk@tut.by>
Reviewed-on: http://review.couchbase.org/33753
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>