generic/299: make sure fio really exits

generic/299: make sure fio really exits

Fix two problems in generic/299

1. Remove $seqres.full before test, otherwise the file is growing all
the time.

2. Make sure fio really exits, otherwise fio would block umount. $pid is
the pid of function run_check not fio, sometimes fio is still there when
$pid is dead and blocking umount.

Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Dave Chinner <david@fromorbit.com>