ZTS: Polish online_offline tests
- Kill workload first for faster cleanup.
- Use zpool wait for resilver instead of sleep.
- Remove irrelevant workload from online_offline_003_neg.
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Sponsored by: iXsystems, Inc.
Closes: #17259