COOK-2337: expose environment attribute on gunicorn and celery submodules

Under the hood, application_python uses the supervisor_service LWRP to manage the services configured by its gunicorn and celery LWRPs.

Since the supervisor_service LWRP supports configuring a hash of environment variables through its 'environment' attribute, it would be useful for this attribute to be exposed on application_python's gunicorn and celery LWRPs.