I've managed to keep this change mainly contained to our
self-testing module. The changes here are:
* There are two different variables for tracking "is our orport
reachable".
* We have a new function that says whether we can skip a single
family's orport reachability test; the old function for this now
tells whether we can skip _all_ orport reachability testing.
(The name, router_should_skip_orport_reachability_test, is not
so good. I will rename it later if I can think of a good
replacement.)
* The function that launches orport reachability tests now only
launches the ones that haven't completed.
* The function that notes that we're reachable on an ORPort now
takes a family.
* Various log messages are cleaned up.
