SERVICES: Convert old spawner to new services API

The services API replaces the spawner API is extensible to allow for future
extra types of transactions such as log file opening.  The new API supports
file descriptors being passed for stdin/stdout/stderr and as a result we adapt
the CGI spawner to be able to spawn CGIs using this new API.

Signed-off-by: Daniel Silverstone <dsilvers@digital-scurf.org>