Comment 1 for bug 1495338

Proposed format:

-------------------

volumes:
  1/0:
    provider-id: volume-1-0
    storage: filesystem/0
    attachments:
      machines:
        "1":
          device: loop0
          read-only: false
      units:
        storagetest/0:
          machine: "1"
          location: /srv/filesystem/0
    size: 1024
    persistent: false
    status:
      current: attached
      since: 15 Sep 2015 19:13:50+08:00
  2/1:
    provider-id: volume-2-1
    storage: filesystem/1
    attachments:
      machines:
        "2":
          device: loop1
          read-only: false
      units:
        storagetest/1:
          machine: "2"
    size: 1024
    persistent: false
    status:
      current: attached
      since: 15 Sep 2015 19:14:02+08:00