- the magic is in --single-version-externally-managed to disable
those (easter) egg things...
cf.
https://wiki.debian.org/Python/FAQ#How_should_we_package_Python_eggs.3F
- --root is required so just pass /
- also, python must be called without any path, else it setuptools uses
it as an extra prefix for install... so we munge PATH and call python.
