d-f-s fixes to properly GC volumes

We have a bunch of containers marked as 'created' which never get GCed, occupying a lot of space. Further to that, containers trying to GC volumes themselves caused problems for us doing independent volume GC, as we'd try to remove volumes which were already removed. The two of those stopped us from actually doing any reasonable cleanup.

These two fixes allow us to clean up the old containers, as well as to properly clean up volumes, which has fixed at least packet-m1xl-1.