load configuration from one per-account subdirectory

def _load_account(self, acct_id, acct_dir_path):
        """load configuration from one per-account subdirectory"""
        # setup a default config dict for the account
        self._config[acct_id] = {
            'name': None,
            'role_name': DEFAULT_ROLE_NAME,
            'regions': {}
        }
        # read the account config file
        # @TODO unhandled exception if file doesn't exist or isn't JSON
        with open(os.path.join(acct_dir_path, 'config.json'), 'r') as fh:
            acct_conf = json.loads(fh.read())
        # overwrite defaults with what we read from the account JSON
        self._config[acct_id].update(acct_conf)
        # iterate over contents of the per-account directory
        for region_name in os.listdir(acct_dir_path):
            path = os.path.join(acct_dir_path, region_name)
            # skip anything that isn't a directory
            if not os.path.isdir(path):
                continue
            # load the per-region configs for the account...
            # @TODO - should check that it's a valid region name
            self._load_region(acct_id, region_name, path)