made <source>...</source> and it's sub-elements conditional
made <source>...</source> and it's sub-elements conditional

pradels/vagrant-libvirt,vagrant-libvirt/vagrant-libvirt,infernix/vagrant-libvirt,pradels/vagrant-libvirt,vagrant-libvirt/vagrant-libvirt,infernix/vagrant-libvirt,electrofelix/vagrant-libvirt,electrofelix/vagrant-libvirt,infernix/vagrant-libvirt,electrofelix/vagrant-libvirt,vagrant-libvirt/vagrant-libvirt