Add a chutney network that does reachability tests

Chutney sets AssumeReachability 1 in all its networks.

We should make a network which doesn't set AssumeReachability, so we can test relay reachability changes.

As part of Sponsor 55, we want to make reachability chutney networks part of:

• make test-network
• make test-network-all
• Tor's Travis CI
• Chutney's Travis CI