Condense some test logic and add a comment about renaming

agent/consul/leader_test.go

@@ -987,9 +987,7 @@ func TestLeader_ChangeNodeID(t *testing.T) {
 				failed++
 			}
 		}
-		if got, want := failed, 1; got != want {
-			r.Fatalf("got %d failed members want %d", got, want)
-		}
+		require.Equal(r, 1, failed)
 	})
 
 	// Bring up a new server with s3's name that will get a different ID
@@ -1013,9 +1011,7 @@ func TestLeader_ChangeNodeID(t *testing.T) {
 
 	retry.Run(t, func(r *retry.R) {
 		for _, m := range s1.LANMembers() {
-			if m.Status != serf.StatusAlive {
-				r.Fatalf("bad status: %v", m)
-			}
+			require.Equal(r, serf.StatusAlive, m.Status)
 		}
 	})
 }

agent/consul/state/catalog.go

@@ -376,6 +376,8 @@ func (s *Store) ensureNoNodeWithSimilarNameTxn(tx *memdb.Txn, node *structs.Node
 				return fmt.Errorf("Cannot get status of node %s: %s", enode.Node, err)
 			}
 
+			// Get the node health. If there's no Serf health check, we consider it safe to rename
+			// the node as it's likely an external node registration not managed by Consul.
 			var nodeHealthy bool
 			if enodeCheck != nil {
 				enodeSerfCheck, ok := enodeCheck.(*structs.HealthCheck)