fix(v2p): pick the real device line from pvesm path output

_pvesm_alloc_disk ran `pvesm path <vol> 2>&1` and took line 0 as the device
path. With 2>&1 a storage plugin that logs a warning to stderr (e.g. a custom
plugin 'implementing an older storage API') prints it BEFORE the path, so
line 0 is the warning and the real path is missed — _ensure_block_device then
fails and the disk transfer aborts.

Now scan for the line that actually looks like a device path (/dev/...) or a
librbd URI (rbd:...) instead of blindly taking line 0.

Verified end-to-end on a real ESXi->Proxmox->Ceph RBD migration (Windows
Server 2025, 90 GB): the migrated RBD holds a real GPT/UEFI disk (EFI System
+ MSR + NTFS basic-data + WinRE) — data landed on the real block device.

Refs #538

Author: MrMasterbay

pegaprox/core/v2p.py

@@ -3280,7 +3280,13 @@ def _pvesm_alloc_disk(pve_mgr, node, storage, vmid, disk_index, size_bytes, errb
             # volume exists, regardless of the alloc command's rc/warnings.
             rc_p, out_p, _ = _pve_node_exec(pve_mgr, node,
                 f"pvesm path {shlex.quote(vol_id)} 2>&1", timeout=10)
-            dev_path = str(out_p or '').strip().split('\n')[0]
+            # NS 2026-07-17: `2>&1` merges stderr, so a mis-behaving storage plugin's
+            # warning (e.g. a custom plugin "implementing an older storage API") can be
+            # printed BEFORE the path and mask it. Pick the line that actually looks like
+            # a device path / librbd URI rather than blindly taking line 0.
+            _plines = [l.strip() for l in str(out_p or '').split('\n') if l.strip()]
+            dev_path = next((l for l in _plines if l.startswith('/') or l.startswith('rbd:')),
+                            (_plines[0] if _plines else ''))
             if dev_path.startswith('/') and rc_p == 0:
                 # MK 2026-06-10 (#538 oetti77 / #272): `pvesm path` only computes the path
                 # string; for RBD (and other block storages) the kernel device isn't mapped