Directory Authorities should test reachability of relays in their family

Sebastian reported on #tor-dev that directory authorities can't set MyFamily, because it makes the relays in the family get marked as not Running.

I'm not sure if this restriction is in the connecting code on authorities or relays, or the accepting code on relays.

If it's on the connecting side, we can disable it on authorities.

If it is in the accepting code on relays, maybe we need to keep it as a defence in depth measure. But we could disable it for authority IP addresses. (It wouldn't work with multiple authority IPs or OutboundBindAddress, but that's getting obscure.)