MB-23086: Clean-up of the stopTaskGroup call.
MB-23086: Clean-up of the stopTaskGroup call.

1) We should ask for every task to be stopped, not just NONIO
2) We no longer need explicit cancels after calling stopTaskGroup

Change-Id: Icf401183d32f9fbf383def95e10887cb50074597
Reviewed-on: http://review.couchbase.org/115588
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Dave Rigby <a09264da4832c7ff1d3bf1608a19f4b870f93750@couchbase.com>

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