Code review comment for ~paride/autopkgtest-cloud:clean-alien-packages

To reviewers: note the usage of -o Dpkg::Options::="--force-confnew". My idea is that if we *downgrade* a package we want the "new" config files (i.e. those from the *older* package, the one being installed), as the already installed conf files may not be supported by the older package version.