sdev backing store nodes not always present
The fundamental problem here is that sdev is inconsistent with when it creates various backing store nodes. This could lead to it not finding some of them down the line. This was fixed such that either a node always has a backing store and that is passed down the directory tree starting with /dev or it is a dynamic node and thus can never have one. I changed the way these flags are propagated to enforce that and to ensure that this cannot happen again.