Allow the fallback directory schedules to be changed outside a test network

In #4483 (moved), I made the additional schedules TestingTorNetwork. But, if it turns out they need tuning, we want to be able to change them in the default torrc in a Tor Browser release.

So they need to be turned into non-testing torrc options, and the testing values moved to the common chutney template.

This also involves carefully sanity checking any user-supplied values to these options.