This ticket is an alternative to legacy/trac#33582 or legacy/trac#33222. Instead of fixing bridge descriptor uploads, we can check bridge logs to make sure that reachability self-tests have succeeded. For consistency, we should also do the same checks for relays. We can only do these tests on authorities, relays, and bridges that are configured with `AssumeReachable 0`. Chutney's current defaults are: * directory authorities: 1 * bridge authorities: 1 * relays: 0 * bridges: 0 * clients: clients never perform reachability self-tests Some custom chutney networks may set `AssumeReachable 1` for relays and bridges. So we should make it easy for them to disable these checks.