eks/*: allow duplicate create calls

[gyuho]

c.f. #123

[gyuho]

On second thought, this kind of change is getting too manual... Seems better to go with generic wrapper for Create + Update calls:

https://github.com/aws/aws-k8s-tester/blob/master/pkg/k8s-client/k8s.go#L206-L225

aws-k8s-tester/pkg/k8s-client/k8s.go

Lines 206 to 225 in 8f65783

	// CreateNamespace creates a single namespace with given name.
	func CreateNamespace(lg *zap.Logger, c clientset.Interface, namespace string) error {
	createFunc := func() error {
	lg.Info("creating namespace", zap.String("namespace", namespace))
	ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
	_, err := c.CoreV1().Namespaces().Create(ctx, &v1.Namespace{ObjectMeta: metav1.ObjectMeta{Name: namespace}}, metav1.CreateOptions{})
	cancel()
	if err == nil {
	lg.Info("created namespace", zap.String("namespace", namespace))
	return nil
	}
	if apierrs.IsAlreadyExists(err) {
	lg.Info("namespace already exists", zap.String("namespace", namespace), zap.Error(err))
	return nil
	}
	lg.Warn("failed to create namespace", zap.String("namespace", namespace), zap.Error(err))
	return err
	}
	return RetryWithExponentialBackOff(RetryFunction(createFunc, Allow(apierrs.IsAlreadyExists)))
	}