Add new Cockpit login needle using the text box area
    
    The background seems to be different in different tests, even
    the reduced area I tried most recently seems to be different in
    some runs. So let's just match in the text area instead. This
    captures some "Fedora" text so it should still notice if branding
    is broken.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>