t/zbd: test that zone_reset_threshold calculation is correct

t/zbd: test that zone_reset_threshold calculation is correct

The option "zone_reset_threshold" specifies the ratio of logical blocks
with data to trigger zone resets. When the I/O range includes
conventional zones, only blocks in sequential zones must be used to
track this value. A recently fixed bug has uncovered that the number of
blocks in conventional zones were erroneously counted as the blocks
with data.

To prevent future regressions, add a test case to confirm that the
logical blocks accounting does not include conventional zones.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>