t/zbd: test random I/O direction in all-conventional case

t/zbd: test random I/O direction in all-conventional case

The number of 'sectors with data' is counted and used to determine the
direction of the first I/O of a random read/write ZBD workload. To
initialize the number, min_zone and max_zone fields in struct fio_file
are referred. There was a code bug that was recently fixed where
min_zone and max_zone fields were not initialized when all zones in I/O
region were conventional zones. This led to an uninitialized number of
sectors with data, and the write direction was always set for random
workloads.

Add a test case to perform random read/write workload on an I/O region
with both sequential and conventional zones. Check that both read and
write I/Os are executed.

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>