ep_perfsuite: include warmup stats if warmup is enabled
ep_perfsuite: include warmup stats if warmup is enabled

This whole stanza was initially removed unconditionally, but we should
check for it as long as warmup is available.

Change-Id: I5e264c06a447aed4aff834241f439edcc12adffc
Reviewed-on: http://review.couchbase.org/72520
Tested-by: buildbot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Manu Dhundi <158873d90a7ef40f3637a222b7329c09d0222554@couchbase.com>

couchbase/ep-engine,couchbase/ep-engine,daverigby/kv_engine,daverigby/kv_engine,membase/ep-engine,membase/ep-engine,couchbase/ep-engine,daverigby/kv_engine,couchbase/ep-engine,membase/ep-engine,daverigby/kv_engine,membase/ep-engine