[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.

from cubicweb.cwctl import run
import sys

run(sys.argv[1:])