* This includes those instances that may be started outside Hudson.
*/
public int countCurrentDockerSlaves(String ami) throws Exception {
final DockerClient dockerClient = connect();
List<Container> containers = dockerClient.containers().finder().allContainers(false).list();
if (ami == null)
return containers.size();
List<Image> images = dockerClient.images().finder().allImages(true).filter(ami).list();