Fix: skip unmanaged nodes in libvirt provider module (#1552)

Author: sdargoeuves

netsim/providers/__init__.py

@@ -329,6 +329,8 @@ def mark_providers(topology: Box) -> None:
 
   for l in topology.links:                          # Set 'providers' attribute on all links
     for intf in l.interfaces:
+      if intf.node not in topology.nodes:
+        continue
       node = topology.nodes[intf.node]
       l.provider[node.provider] = True