t/zbd: rename logical_block_size to min_seq_write_size

t/zbd: rename logical_block_size to min_seq_write_size

The test script t/zbd/test-zbd-support assumes that the logical block
size is the minimum size unit to write to sequential write required
zones, then it uses a variable named 'logical_block_size' to keep the
minimum size. The assumption is true for ZNS devices but not for ZBC/ZAC
devices. Rename the variable from 'logical_block_size' to
'min_seq_write_size' to not imply the wrong assumption.

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