Add a required version setting to chutney (or to chutney networks)
This is important when we add a new chutney feature or network (like in legacy/trac#20069 (moved)), then make Tor depend on it.
One way we could do this is to check the exit status of chutney in chutney/chutney, and logging the appropriate message if it fails.
Another way is for the Tor chutney tests to set CHUTNEY_MIN_VERSION, and then chutney warns if it's not that version. This would actually require us to version chutney.