[devtools] Adjust skeleton setup.py to have it read information from __pkginfo__.py
Since the later is now installed in cubicweb_<CUBENAME> directory.
Add a test ensuring that `python setup.py sdist` works on newly created cube
(which should at least verify that setup.py is valid).
Related to #13001466.
missing-dep-for-interpreter make => make | build-essential | dpkg-dev (usr/*/cubicweb/skeleton/debian/rules)