code: @Override
    public Set<PackingPlan.ContainerPlan>
        addContainers(Set<PackingPlan.ContainerPlan> containersToAdd) {
      controller.addContainers(containersToAdd);
      return containersToAdd;
    }
docs: Add containers for a scale-up event from an update command
  
  @param containersToAdd the list of containers that need to be added
  
  NOTE: Due to the mechanics of Kubernetes pod creation, each container must be created on
  a one-by-one basis. If one container out of many containers to be deployed failed, it will
  leave the topology in a bad state.
  
  TODO (jrcrawfo) -- (https://github.com/apache/incubator-heron/issues/1981)