t/zbd: Support testing zone capacity smaller than zone size

t/zbd: Support testing zone capacity smaller than zone size

Add support for testing zoned block devices where zone capacity is less
than zone size. If the test case runs sequential workloads or workloads
with verify, use zone capacity instead of zone size to complete.

To use zone capacity of the test target zones, introduce a helper
function total_zone_capacity() which sums up zone capacity numbers of the
test target zones.

Reviewed-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Hans Holmberg <hans.holmberg@wdc.com>
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>