Allows chef node and client deletion

These changes are required for new foreman-chef feature allowing user to delete nodes and clients (host certificates in puppet terminology) upon host deletion in foreman. I'm starting to wonder whether we should extract chef into a separate proxy plugin soon.
hmm. Chef module is mounted under 'api'; You are adding another prefix here -- 'chefproxy'. I think we should have just one, 'chefproxy' (or just 'chef'?).