Fix virtualbox guest modules build

Tails 0.17.1 brings a regression: VirtualBox guest modules are not built during the Tails ISO build. We should fix this.

Feature Branch: bugfix/fix_virtualbox_dkms_build

Original created by @tails on 5972 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information