Add a benchmark that exercises only successful Add-s.
Add a benchmark that exercises only successful Add-s.

Change-Id: I75ff2e042dcf280c57f6f350bf459e15873471a2
Reviewed-on: http://review.couchbase.org/104931
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Tested-by: Aliaksey Artamonau <ce14b1c16e0fd654f926118eb8addbec5aff4ffa@couchbase.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>

couchbase/cbauth,couchbase/cbauth