t/zbd: get max_open_zones from sysfs

t/zbd: get max_open_zones from sysfs

The helper bash function gets max_open_zones limit of the test target
device using sg_inq and libzbc tools. This works for SAS/SATA devices
but does not work for ZNS or null_blk devices. This results is running
the test case 31 with wrong max_open_zones value. Fix this by referring
max_open_zones sysfs attribute.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/r/20230719105756.553146-10-shinichiro.kawasaki@wdc.com
Signed-off-by: Vincent Fu <vincent.fu@samsung.com>