code: synchronized Container removeAndGet(final String containerId) {
      final Container result = this.containers.remove(containerId);
      if (null == result) {
        throw new RuntimeException("Unknown container to remove: " + containerId);
      }
      return result;
    }
docs: Removes the container with the given ID.
  
  @param containerId
  @return the container that was registered before.
  @throws java.lang.RuntimeException if no such container existed.