def project_closed(self, project):
        """
        Called when a project is closed.

        :param project: Project instance
        """

        yield from super().project_closed(project)
        hdd_files_to_close = yield from self._find_inaccessible_hdd_files()
        for hdd_file in hdd_files_to_close:
            log.info("Closing VirtualBox VM disk file {}".format(os.path.basename(hdd_file)))
            try:
                yield from self.execute("closemedium", ["disk", hdd_file])
            except VirtualBoxError as e:
                log.warning("Could not close VirtualBox VM disk file {}: {}".format(os.path.basename(hdd_file), e))
                continue
Called when a project is closed.

        :param project: Project instance