I downloaded ubuntu16.04 template from template browser and then I created a VPS on my proxmox node. It works completely OK (network, root password, vnc, etc.).
The only big problem is it doesn't partition hard-disk well.
It only creates a partition as much as root needs.
For example when I create a 50GB hard-disk VPS, it only a creates an 1.2GB partition and doesn't care about the remaining 48.8GB.