The installer and the manual installation install four systemd units
(webvirt-cloud, webvirt-novncd, webvirt-socketiod, webvirt-worker) that
run as the web server's user with absolute paths and read
/etc/default/webvirtcloud. gunicorn, socketiod and the worker stop with
KillMode=mixed, so they wind down their own children. supervisor, its
installer code and the contributed systemd files go; the README gets
the update, rollback and a one-time move from supervisor, and the
installer refuses to run over a supervisor install. Docker keeps runit;
novncd's runit script is the one-line form of the others.
