Start all the registered services.

        A new container is created for each service using the container
        class provided in the __init__ method.

        All containers are started concurrently and the method will block
        until all have completed their startup routine.

def start(self):
        """ Start all the registered services.

        A new container is created for each service using the container
        class provided in the __init__ method.

        All containers are started concurrently and the method will block
        until all have completed their startup routine.
        """
        service_names = ', '.join(self.service_names)
        _log.info('starting services: %s', service_names)

        SpawningProxy(self.containers).start()

        _log.debug('services started: %s', service_names)