When the processes are started outside of the init system and
that init system is systemd, the documented procedure to stop
foundationdb (`sudo service foundationdb stop`) does not work.
This fixes the issue by creating the service unit and starting it
with systemd when possible.
It was only listed as a dependency due to make_public.py, and means that
installation fails on a fresh install of Ubuntu, so Python is being
demoted to a Recommended package instead of required one.
Chris Donati