Wait till we reach hub after setting root password
    
    Lately anaconda can take up to 10 seconds to exit the root pw
    spoke, which can defeat the subsequent `wait_still_screen` that's
    meant to wait out the 'slide-in-from-the-top' animation of the
    hub. So let's assert the hub after we click Done, then the still
    screen wait will only happen *once the hub is visible* and should
    really do its job.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>