http server:
  - http_servers() emited server objects: rename server attribute into http_server
    to emphizize that this is an instance of http.Server.
  - HTTP_Server_Handler(): remove unused end_point parameter
  - implement virtual_http module (embeddeed for now) to really virtualize socket.io
    and provide the basis for many other uses cases. This vitual http module is a
    good candidate to extract as a standalone module.
  - implement virtual_http_servers() pipelet using embeded virtual_http module
  - to test these, we now need to modify the HTTP_Server_Handler() logic.