CBD-807: add reb-vperf config with stale=ok queries

Change-Id: I4f95f9f0bca2f90d1331b088ef30a95c999e1533
Reviewed-on: http://review.couchbase.org/24351
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>