Enhance the E2E test to be runnable against remote clusters on e.g. AWS EKS (#1610)

This contains apparently enough changes to the current E2E test code to make it runnable against remote Kubernetes clusters. I was actually able to make the test passing against my AWS EKS based test clusters with these changes. You still need to trigger it manually from a local checkout of the ARC repo today. But this might be the foundation for automated E2E tests against major cloud providers.

testing/docker.go

@@ -71,3 +71,18 @@ func (k *Docker) dockerBuildCombinedOutput(ctx context.Context, build DockerBuil
 
 	return k.CombinedOutput(cmd)
 }
+
+func (k *Docker) Push(ctx context.Context, images []ContainerImage) error {
+	for _, img := range images {
+		_, err := k.CombinedOutput(dockerPushCmd(ctx, img.Repo, img.Tag))
+		if err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+func dockerPushCmd(ctx context.Context, repo, tag string) *exec.Cmd {
+	return exec.CommandContext(ctx, "docker", "push", repo+":"+tag)
+}