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.