code: func (c *Cluster) ExportContainer(opts docker.ExportContainerOptions) error {
  	node, err := c.getNodeForContainer(opts.ID)
  	if err != nil {
  		return err
  	}
  	return wrapError(node, node.ExportContainer(opts))
  }
docs: // ExportContainer exports a container as a tar and writes
  // the result in out.