It would be nice if we support websocket protocal `ws and wss` as a private base URL in the backend.

We can then modify Apicast to add the policy for https://www.nginx.com/blog/websocket-nginx/. It pretty easy and straightforward.

*Current behavior:*
When I try to add the echo ws backend wss://echo.websocket.org it results in error
`The accepted format is 'protocol://address(:port)'`

*Expected result:*
Both http and ws should be supported, as we see more usecases around webscoket API and support using APIcast.

See also THREESCALE-916