The storage deduplication logic only checked cluster config's Shared
flag, but this required the cluster config API call to succeed. When
the per-node storage API already returns shared=1 (as the user
verified), we should use that directly.
Now we check three sources for shared storage detection:
1. Per-node API shared flag (storage.Shared)
2. Cluster config shared flag (if available)
3. Storage type heuristics (NFS, RBD, PBS, etc.)
Related to #1049
rcourtman
9cfcdbb247