Create the device service cluster group and add devices to it.

def create(self, **kwargs):
        '''Create the device service cluster group and add devices to it.'''

        self._set_attributes(**kwargs)
        self._check_type()
        pollster(self._check_all_devices_in_sync)()
        dg = self.devices[0].tm.cm.device_groups.device_group
        dg.create(name=self.name, partition=self.partition, type=self.type)
        for device in self.devices:
            self._add_device_to_device_group(device)
            device.tm.sys.config.exec_cmd('save')
        self.ensure_all_devices_in_sync()