delayed delete volume

Currently glance and nova hava the feature of delayed deleting of resouce, which enable users to delete image or vm in a delayed time, in case of user's regrete deleting. Cinder should import this feature to enable delayed deleting. With a delayed deleting of volume, the volume is deleted and quota of this volume is freed, but the volume is not deleted actually, in the delayed time(FE 2hours), user can restore this volume in recycle, and if the volume is not restored, it will be deleted acutually beyond the delayed time.