ssh IPs conflicts for libvirt when instances are run from the same box Ubuntu 17 at the same time (packer build -only=qemu ubuntu-17.10-amd64.json ; vagrant box add --name name box_name.box)
NetPlan is a new network configuration tool introduced in Ubuntu 17.10 to manage networks.
The MAC address of the interface of the virtual machine is used to manage network. (https://github.com/vagrant-libvirt/vagrant-libvirt#management-network. Last paragraph)
It can be fixed by the following scripts
https://github.com/AlexeyAlexey/packer-templates/blob/master/scripts/ubuntu/upgrade.sh (it is important)
https://github.com/AlexeyAlexey/packer-templates/blob/master/scripts/ubuntu/networking.sh