Code review comment for lp:~jelmer/loggerhead/drop-python3

Same comment as in https://code.launchpad.net/~jelmer/loggerhead/fix-tox/+merge/411874 - could you adjust this to keep Python 3.5? I'll need to merge these two together, since something (probably a Breezy release or similar) has broken the Python 2 tests.

We'll need to upgrade Launchpad to Breezy >= 3.1, but that should be manageable now.