zbd, verify: verify before zone reset for zone_reset_threshold/frequency

zbd, verify: verify before zone reset for zone_reset_threshold/frequency

When zone_reset_threshold and zone_reset_frequency options are specified
with zonemode=zbd, it resets zones not full. When verify option is
specified on top of that, the zone reset of non-full zones erases data
for verify and causes verify failure. Current implementation avoids this
scenario by assert.

To allow zone_reset_threshold/frequency options together with verify,
do verify before the zone reset. When zone reset is required to an open
zone with verify data, call get_next_verify() to get io_u for verify
read and return it from zbd_adjust_block(). When io_u->file is set,
get_next_verify() assumes the io_u is requeued and does nothing. Unset
io_u->file to tell get_next_verify() is not requeued.

Also modify verify_io_u() to skip rand_seed check when the option
zone_reset_frequency is set. When the option is set, random seed is not
reset for verify reads in same manner as verify_backlog option, then
this check is not valid.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Vincent Fu <vincent.fu@samsung.com>