MB-100: tune cache misses

Change-Id: I368ea0727bc541bcff274ba3140380ff5325a201
Reviewed-on: http://review.couchbase.org/27475
Reviewed-by: Ronnie Sun <ronnie@couchbase.com>
Tested-by: Ronnie Sun <ronnie@couchbase.com>
Tested-by: buildbot <build@couchbase.com>