Avoid spurious repo check error for universal tests on netinst
    
    As there is *always* a base repo error when booting a netinst
    image, this check was giving us spurious failures when running
    universal tests on a netinst (which we are currently doing on
    ppc64 it seems). Tweak it a bit to hopefully avoid this.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>