Handle 'authentication required' appearing on Boxes startup
    
    In the last few weeks Boxes is showing an auth dialog on start.
    I've filed a bug on this; let's have the test handle it as a
    soft failure, since this isn't a fatal problem. Do this by
    making an existing needle for this dialog a bit more generic
    in name and using it.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>