MB-100: increase target throughput for test with cache misses

Change-Id: Ia59faa4a6f163a24d5368040095b444d52b88623
Reviewed-on: http://review.couchbase.org/25221
Reviewed-by: Pavel Paulau <pavel.paulau@gmail.com>
Tested-by: Pavel Paulau <pavel.paulau@gmail.com>