Catch 404s when deleting default networks.

As seen in hashicorp/terraform-provider-google#3582, it is now
possible to set an organization policy that removes the default network
from a project when it's created. This means it's now possible that
Terraform's attempt to delete that default network will encounter an
error saying the network is not found. Because what Terraform wanted was
achieved, even if not by Terraform, we shouldn't raise that error, we
should ignore it.

third_party/terraform/resources/resource_google_project.go

@@ -263,7 +263,11 @@ func resourceGoogleProjectCreate(d *schema.ResourceData, meta interface{}) error
 		}
 
 		if err = forceDeleteComputeNetwork(project.ProjectId, "default", config); err != nil {
-			return fmt.Errorf("Error deleting default network in project %s: %s", project.ProjectId, err)
+			if isGoogleApiErrorWithCode(err, 404) {
+				log.Printf("[DEBUG] Default network not found for project %q, no need to delete it", project.ProjectId)
+			} else {
+				return fmt.Errorf("Error deleting default network in project %s: %s", project.ProjectId, err)
+			}
 		}
 	}
 	return nil