To enable tun device in OpenVZ containers tun module

• needs to be loaded in the host system (in my case CentOS 6.4)
• containter (in my case Ubuntu Server 12.04) must be allowed to use tun

This howto is based on two sources: Official wiki and Amutu blog entry. In short, the main difficulty is in bridge network configuration: correct network configuration doesn’t work in CentOS 6.4 while NetworkManager is running. I compiled official documentation and fix found in Amutu blog here in one entry.