Close httplib2 connections.

Create a BatchHttpRequest object based on the discovery document.

                Args:
                  callback: callable, A callback to be called for each response, of the
                    form callback(id, response, exception). The first parameter is the
                    request id, and the second is the deserialized response object. The
                    third is an apiclient.errors.HttpError exception object if an HTTP
                    error occurred while processing the request, or None if no error
                    occurred.

                Returns:
                  A BatchHttpRequest object based on the discovery document.