cockpit: don't try and get admin privs when re-logging in
    
    There's one point in the tests where we may log into cockpit for
    the second time in one run (it depends how a package update
    process goes). When this happens, we don't get prompted again
    for admin access, so we need to *not* expect that.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>