zbd: fix sequential write pattern with verify= and max_open_zones=

zbd: fix sequential write pattern with verify= and max_open_zones=

Sequential write with max_open_zones=1 has interesting (read: buggy)
interaction with verify=.

If verify is off, then job runs correctly and IO is sequential,
and restarted from offset 0 and remains sequential.

If verify is on, then 1 full run is done and verified correctly.
At this point there is exactly 1 open zone which is the last zone.

Now IO restarts from offset 0 and pick_random_zone() picks opened zone
#0 which is the last zone because offset is 0. All IO is redirected
to the last zone, which is rewritten once triggering verify again.

IO pattern becomes: 1 full sequential rewrite followed by constant
sequential rewrites of the last zone.

	[global]
	filename=/dev/loop0
	direct=1
	zonemode=zbd
	zonesize=1M
	bs=512K
	rw=write
	verify=xxhash
	[j]
	max_open_zones=1
	io_size=3G

Fix is to close every zone given that verification acts as a barrier
between jobs.

max_open_zones=2 can restart from half of the device, etc.

Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Alexey Dobriyan (SK hynix) <adobriyan@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>