MB-7074: add experimental xperf configs

Change-Id: I805cf1b7dd8f5c59d46e5a892cb58ce66a1b174c
Reviewed-on: http://review.couchbase.org/24256
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>