application: make ensure_controller private
application: make ensure_controller private

I'm not sure where the idea of sub classing application came from,
but we are definitely not doing nor will we need to any time soon.

If we make this a private function we can start using private data
there, which we will in a sec.
https://phabricator.endlessm.com/T13538

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib