Assimilate the entire subdirectory structure in rootpath.

def parallel_assimilate(self, rootpath):
        """
        Assimilate the entire subdirectory structure in rootpath.
        """
        logger.info('Scanning for valid paths...')
        valid_paths = []
        for (parent, subdirs, files) in os.walk(rootpath):
            valid_paths.extend(self._drone.get_valid_paths((parent, subdirs,
                                                            files)))
        manager = Manager()
        data = manager.list()
        status = manager.dict()
        status['count'] = 0
        status['total'] = len(valid_paths)
        logger.info('{} valid paths found.'.format(len(valid_paths)))
        p = Pool(self._num_drones)
        p.map(order_assimilation, ((path, self._drone, data, status)
                                   for path in valid_paths))
        for d in data:
            self._data.append(json.loads(d, cls=MontyDecoder))