t/zbd: Align block size to zone capacity

t/zbd: Align block size to zone capacity

The test cases #5, #6, #15 and #37 writes data and read it back (or
write with verify option for read back). When test target zones have
zone capacity unaligned to the block size, read request can not be made
to all of the written data, and the test cases fail.

To avoid the failures, check zone capacity of zones and get block size
which can align to the zone capacities. Then use the block size for the
test cases.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Reviewed-by: Niklas Cassel <niklas.cassel@wdc.com>
Link: https://lore.kernel.org/r/20211013060903.166543-5-shinichiro.kawasaki@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>