Work out how to fail chutney travis jobs when the tor repository is out of date or missing
In #27912 (moved), we configure a bunch of deb lines that depend on deb.torproject.org. But what happens when the repository is updated after a release?
We can either:
- remember to update the travis config every release, or
- work out how to make the jobs fail when they fall back to 0.2.9.14 (or Ubuntu security updates' current version)
Maybe there's a travis option that we could use?
This task does not need to be solved straight away.