Speed up test_access_scanner under TSan by ~10x
Speed up test_access_scanner under TSan by ~10x

test_access_scanner creates a number of items to push residency down
to under 90%. When run under ThreadSanitizer this takes a while (12s
on local server, seen 2-3x that on CV machines).

We can speed it up by creating fewer, larger items.

Before:
    real    0m12.432s

After:
    real    0m0.892s

Change-Id: I53cf666c9841accd3f2f7f4da1d5ee8dcfc022af
Reviewed-on: http://review.couchbase.org/64035
Reviewed-by: Will Gardner <cbd6f5d9092d9ef7d5c0510d53bba134b22c02f2@couchbase.com>
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

owendCB/ep-engine,owendCB/ep-engine,hisundar/ep-engine,couchbase/ep-engine,owendCB/ep-engine,daverigby/kv_engine,teligent-ru/ep-engine,daverigby/kv_engine,couchbase/ep-engine,hisundar/ep-engine,couchbase/ep-engine,daverigby/kv_engine,membase/ep-engine,daverigby/ep-engine,daverigby/ep-engine,daverigby/kv_engine,teligent-ru/ep-engine,owendCB/ep-engine,teligent-ru/ep-engine,membase/ep-engine,hisundar/ep-engine,membase/ep-engine,daverigby/ep-engine,couchbase/ep-engine,membase/ep-engine,hisundar/ep-engine,daverigby/ep-engine,teligent-ru/ep-engine