Fix Vagrant basebox building using veewee and KVM

See the blueprint. We have to wait until there’s a new release of veewee, and then there’s some coding to be done.

Blueprint: https://tails.boum.org/blueprint/vagrant-libvirt/

Feature Branch: feature/6354-vagrant-libvirt

Related issues

• Blocks #6354 (closed)

Original created by @anonym on 6356 (Redmine)