harness: Handle -ENOTSUP from io_submit() with RWF_NOWAIT
    
    On filesystems such as tmpfs the syscall might return -ENOTSUP instead
    of EINVAL when it does not support the RWF_NOWAIT flag.
    
    Signed-off-by: Guillem Jover <guillem@hadrons.org>
    [JEM: skip the test instead of returning success]
    [JEM: make the error message differentiate between kernel and fs support]
    Signed-off-by: Jeff Moyer <jmoyer@redhat.com>