ep_perfsuite: Reduce iteration count when running under ASan
ep_perfsuite: Reduce iteration count when running under ASan

Reduce the default interation count for tests in ep_perfsuite when run
under AddressSanitizer. This is the same reduced iteration count which
ThreadSanitizer uses; while ASan isn't typically /as/ slow as TSan
it's still significantly slower than normal.

Wallclock time:

    Before: 1m48.690s
    After:  0m39.886s

Change-Id: I98962740bb18900f1f82b0c65fc44b5d8a0e3382
Reviewed-on: http://review.couchbase.org/97066
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Ben Huddleston <6c0d3f0e87b08a8c49786ca528f2c4b1ad3d36f3@couchbase.com>

daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine,daverigby/kv_engine