Volume created from snapshot can not be migrated/retyped to different backend after snapshot got deleted

Issue

Right now we have the following documented limitation related to Migrate volumes

Migrating volumes that have snapshots are currently not allowed.

But when we:

1. Create volume
2. Create snapshot from volume
3. Create volume from the snapshot
4. Delete snapshot
5. Re-type newly created volume (from the snapshot) which includes storage migration

It fails with:

2017-05-29 03:39:38.413 4196 ERROR cinder.volume.manager SnapshotNotFound: Snapshot 48cf30e7-942a-4c99-a432-cb09a6334d1c could not be found.