OpenBSD support

I have a branch for OpenBSD support. I've seen that you are also working on this, but did not yet merge your branch. My branch is not based on your work as I started it before noticing your branch, but it has the same changes plus some more. I also have a solution for starting the service, so your solution to not enable the service on OpenBSD is not needed.

I'll send two other pull request. If you want to merge them all, there is also an already merged branch in our repository: https://github.com/cirrax/puppet-openvpn/tree/cirrax