Add support for --remote-config

This allows you to tell a fio server to open a local job file,
as opposed to being passed one that the fio client opens and
sends to it.

Signed-off-by: Jens Axboe <axboe@fb.com>
client: remember to zero pad filename

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