MB-100: adjust xperf config

Change-Id: I1f751603e79aa0e5d596f8d4ce31f3c306f097d7
Reviewed-on: http://review.couchbase.org/27046
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>