Build instructions are broken on Jessie
Type of work:
The following packages have unmet dependencies: vagrant-libvirt : Depends: ruby-fog-libvirt (>= 0.3.0) but it is not going to be installed
ruby-fog-libvirt/stretch depends on Stretch's Ruby, that IMO we should not try installing on Jessie.
IMO the best fix is to simply require Stretch.