Update openvpn module

The one on git://github.com/luxflux/puppet-openvpn.git has seen quite some updates (also pushed on https://leap.se/git/puppet_openvpn until recently). The configuration changed (no more openvpn::option), I think at some point we'd need to update/upgrade this submodule too, after almost a year.

(from redmine: created on 2013-09-14)