... provided by Chutney (https://gitweb.torproject.org/chutney.git).
This is enabled iff the local configuration contains something like:

  Chutney:
    src_dir: "/path/to/chutney-src-tree"

otherwise we'll use the real Tor network as we done previously.

The main motivation here is improved robustness -- since the "Tor
network" we now use will exit from the host running the automated test
suite, we won't have to deal with Tor network blocking. Performance
should also be improved.

Will-fix: #9521