support VPS under OpenVZ

[ofit]

Please add support for VPS under OpenVZ. My provider allow tun/tap interface but this script doesn't support install on openVZ. Thanks

[prsly]

@ofit, I think what OpenVPN doesn't install at many providers with OpenVZ

[ofit]

Not agree at all. OpenVZ is cheap and it good for OpenVPN server. About 85% of all OpenVZ that i know have enabled OpenVPN on it.