Make sure all `check_screen` calls have explicit timeout
    
    Upstream is gonna change the default from 30 to 0, it seems:
    https://github.com/os-autoinst/os-autoinst/pull/965
    so let's go ahead and change these two cases where we have no
    explicit timeout to have one.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>