[pkg] Add new autopkgtest for skeleton packaging When running `cubicweb-ctl newcube`, the generated template provides debian packaging. So let's add automated tests for that using autopkgtest. The new test will generated a new cube, build a source tarball, build the package, try to install it, see if the Python 3 module is available and even run autopkgtest against the newly created packages. Along the way it will also print information about the generated package: buildinfo, package content, and lintian report.