Tor options to disable Network Connections to Authorities, IPv4, IPv6

Tor already has DisableNetwork, an option that prevents network connections.

But when testing legacy/trac#15775 (moved) (Fallback Directories), it would be useful to be able to disable connections to the authorities only. (Like the attached torrc.block_authorities file.) This would help us ensure bootstrap works without authorities. DisableDirectDirAuthConnection?

When testing legacy/trac#8374 (moved), it could be useful to disable IPv4, so that we can ensure bootstrap works with only IPv6. This would be like ClientUseIPv6 and ClientPreferIPv6ORPort, but applying strictly to the entire Tor process: DisableIPv6Network.

And it might also be useful to disable IPv6, if IPv6 becomes active by default: DisableIPv4Network.

This would help us cover the IPv4/IPv6 testing combinations listed at the bottom of: https://lists.torproject.org/pipermail/tor-relays/2015-June/007109.html