When multiple PVE instances have VMs with overlapping VMIDs, PBS backups
were being matched to the wrong VM because the code would just use the
first matching guest. Now when a PBS backup has a namespace, it attempts
to match that namespace to the PVE instance name to find the correct VM.
This helps users who have separate PBS instances backing up different
PVE clusters with namespaces like "pve1", "nat", etc.
a88edd7c8f