t/zbd: Add support for libzbc IO engine tests

t/zbd: Add support for libzbc IO engine tests

Modify the test-zbd-support script to accept SG node device files for
tests with the libzbc IO engine. This IO engine can also be tested with
a block device file using the new -l option which forces all test cases
to have the option --ioengine=libzbc.

New helper functions are added to discover the capacity, logical block
size etc of devices specified using an SG node file.

To facilitate troubleshooting of problems, the option -z is also added
to automatically add the option --debug=zbd to all test cases.

Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>