[server] refactor cleanup() code used by "cubicweb-ctl delete"
Try to make each logical step (i.e. "delete database" and "delete user")
a bit more visible and explicit.
This is a preparatory work to easily plug the "delete namespace" feature.
.. -*- coding: utf-8 -*-
Server Architecture
-------------------
.. image:: images/server-class-diagram.png
`Diagramme ArgoUML`_
[FIXME]
Make a downloadable source of zargo file.
.. _`Diagramme ArgoUML`: cubicweb.zargo