Homu only works on a python3 toolchain. Our salt configuration does not autoinstall this.

Homu worked so far because it somehow had a python3 virtualenv with everything it needed, without a global install of any of the python3 tools.

Specifically, we need:

sudo apt-get install python3.4 python3-pip
pip3 install virtualenv

We can do the former with a - require: - pkg: key in homu.sls somewhere.

I'm not sure how to indicate a pip3-specific dependency, though. Perhaps something with bin_env?

We also need to make sure that the pip/python/virtualenv setup does not make 3.4 the default for the pip/python/virtualenv binaries. Installing them as shown above seemed to preserve the default, but I'm not sure if that's something we can rely on.

cc @edunham @larsbergstrom