code: func buildDockerImage(imageDir, imageName string) {
  	if dockDir == "" {
  		panic("dockDir should be set before calling buildDockerImage")
  	}
  	cmd := exec.Command("docker", "build", "-t", imageName, ".")
  	cmd.Dir = filepath.Join(dockDir, imageDir)
  	cmd.Stdout = os.Stdout
  	cmd.Stderr = os.Stderr
  	if err := cmd.Run(); err != nil {
  		log.Fatalf("Error building docker image %v: %v", imageName, err)
  	}
  }
docs: // buildDockerImage builds a docker image from the Dockerfile located in
  // imageDir, which is a path relative to dockDir. The image will be named after
  // imageName. dockDir should have been set behorehand.