add service provider for OpenBSD

Adds a service provider for OpenBSD. This was split off of another pull request: #2177. This initial commit has the proposed logic in place. I copied the tests from the FreeBSD provider and fixed them, but that's not good enough--the tests don't yet cover what they need to. I'll be taking another pass at them, but I didn't want to wait on that to get the discussion started on the rest of the code.
Makes sense. I'm going to rip out the current implementation of this idea and I'll consider filing a future PR to add it back if it makes sense. For now I think its better to keep it simple, and I believe this provider is good step forward without it.