diskutil: try additional slave device path if first fails

diskutil: try additional slave device path if first fails

Running fio on an NVMEoF device with multipath slaves fails with a "No
such file or directory" error when displaying disk stats. Correct this
by using a different path to the sysfs slave device.

[sitsofe: change new path to be a fallback when regular path fails]

Fixes: https://github.com/axboe/fio/issues/525
Closes: https://github.com/axboe/fio/pull/526

Signed-off-by: Potnuri Bharat Teja <bharat@chelsio.com>
Signed-off-by: Sitsofe Wheeler <sitsofe@yahoo.com>