options: turn missing options into debug parse messages

options: turn missing options into debug parse messages

It's not an error, we expect it to happen if we try and check
for set options that aren't available (due to being platform
specific, libraries missing, etc).

This fixes cases where fio would spew:

fio: no option found at offset 1240

and other offsets.

Signed-off-by: Jens Axboe <axboe@fb.com>