[DF] Fallback to FindBranch if GetBranch fails in Snapshot
[DF] Fallback to FindBranch if GetBranch fails in Snapshot

FindBranch might find "exotic" branch names that GetBranch does not.

This also makes the branch-searching logic of Snapshot more consistent
with what we do in other places.

root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,olifre/root,olifre/root,root-mirror/root,root-mirror/root