###Get Ubuntu minimal in OpenVZ from here http://download.openvz.org/template/precreated/ Lots of VZ templates here (many more than you can install from Proxmox interface)
Follow this guide to configure the network (which won't work out of the box) https://openvz.org/Ubuntu_without_templates
Stop using vmbr and use veth instead! Then you can configure ubuntu/debian just like a baremetal server with a static IP https://help.ubuntu.com/lts/serverguide/network-configuration.html#ip-addressing