Vagrantfile: Allow libvirt vm build
This adapts the README to describe the necessary tooling. And adds a qemutest vm to use libvirt as provider (instead of vbox).
Runs fine as demonstrated in migrated/migration$799.
First iteration failed without the gpg dependency ~> migrated/migration$797 Thus why the post-install.sh adds it directly as a workaround (in this diff).
Ideally, this should be added in our manifest somewhere or even better in the puppet module which requires it but I don't know which one is pulling it ¯_(ツ)_/¯. In the mean time, that sounds reasonable.
Note: As migrated/migration$798 shows, it is not required for the vbox template and I don't know why this worked for it.
Depends on !28 (closed)
Related to T2606
Test Plan
vagrant destroy qemutest --force; vagrant up qemutest
output: migrated/migration$799
Migrated from D4138 (view on Phabricator)