'Creates the app.yaml file in WEB-INF/appengine-generated/.
Returns:
The path to the WEB-INF/appengine-generated directory.'

def _GenerateAppYaml(self, stage_dir, api_version, appengine_generated):

    static_file_list = self._GetStaticFileList(stage_dir)
    yaml_str = self.GenerateAppYamlString(static_file_list, api_version)
    if (not os.path.isdir(appengine_generated)):
        os.mkdir(appengine_generated)
    with open(os.path.join(appengine_generated, 'app.yaml'), 'w') as handle:
        handle.write(yaml_str)
