Add more context to the error messages

Errors like:

fio: pid=0, err=22/file:filesetup.c:380, error=Invalid argument

do not give a lot of clue as to what is wrong, unless you
have a matching source. So add a context relevant info
message as well.

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