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.
We have `/api/reports` and `/api/hosts/facts` that are for uploading data from chef-client to foreman. The API is on same path as it is on foreman so in chef-client you can use either of them. The `/api/chefproxy/*` is for the other direction - foreman communicating to chef-server.