Updates settings of instance <name> with the
            dictionary <settings>.

def update_instance(self, name, settings):
        """ Updates settings of instance <name> with the
            dictionary <settings>. """
        if name not in self.insts:
            raise ValueError("There's no instance named %s" % name)
        if 'module' in settings:
            raise ValueError(("Can't change module of existing instan"
                              + "ce %s") % name)
        self.l.info('update instance %-15s' % (name))
        for k, v in six.iteritems(settings):
            self.change_setting(name, k, v)