Get the device group through a device.

        :param device: bigip object -- device
        :returns: tm.cm.device_groups.device_group object

def _get_device_group(self, device):
        '''Get the device group through a device.

        :param device: bigip object -- device
        :returns: tm.cm.device_groups.device_group object
        '''

        return device.tm.cm.device_groups.device_group.load(
            name=self.name, partition=self.partition
        )