Register CORS options endpoints.

def _register_options(self, api_interface):
        # type: (ApiInterfaceBase) -> None
        """
        Register CORS options endpoints.
        """
        op_paths = api_interface.op_paths(collate_methods=True)
        for path, operations in op_paths.items():
            if api.Method.OPTIONS not in operations:
                self._options_operation(api_interface, path, operations.keys())