smart proxy discovery

Overall I agree but I am not so sure about this structure.

I think that `DiscoveryRequest` class is not neccessary, just use `ForemanRequest` directly in the `create_discovered_host` method.

For all the other methods, I would create new helper class similar to `ForemanRequest`, but without all the SSL configuration. It would be very similar, but I would not use inheritance in this case, it is a different class. Or maybe you can keep it as is if that turns to be overengineering. My only concern is dupes of these `VERIFY_NONE` lines. This could be encapsulated in the class.

Unfortunately I am not able to start testing this today, too late for me.