Use id_order=True on vf2_mapping() for VF2Layout pass

Using id_order=False orders the nodes by degree which biases the
mapping found by vf2 towards nodes with higher connectivity which
typically have higher error rates. Until the pass is made noise aware
to counter this bias we should just use id_order=True which uses the
node id for the order (which roughly matches insertion order) which
won't have this bias in the results.

qiskit/transpiler/passes/layout/vf2_layout.py

@@ -30,7 +30,7 @@ class VF2LayoutStopReason(Enum):
 
 class VF2Layout(AnalysisPass):
     """A pass for choosing a Layout of a circuit onto a Coupling graph, as a
-    a subgraph isomorphism problem, solved by VF2++.
+    a subgraph isomorphism problem, solved by VF2.
 
     If a solution is found that means there is a "perfect layout" and that no
     further swap mapping or routing is needed. If a solution is found the layout
@@ -93,7 +93,12 @@ def run(self, dag):
         im_graph.add_nodes_from(range(len(qubits)))
         im_graph.add_edges_from_no_data(interactions)
 
-        mappings = vf2_mapping(cm_graph, im_graph, subgraph=True, id_order=False, induced=False)
+        # id_order=True is set here to not use the VF2++ heuristic. VF2++
+        # searches over node in order of degree and thus has a bias towards
+        # picking nodes with more connectivity which typically have higher
+        # noise which means with id_order=False we would have a bias towards
+        # picking qubits with typically higher noise.
+        mappings = vf2_mapping(cm_graph, im_graph, subgraph=True, id_order=True, induced=False)
         try:
             mapping = next(mappings)
             stop_reason = VF2LayoutStopReason.SOLUTION_FOUND