agent/engine/docker_task_engine.go
func (engine *DockerTaskEngine) UnmarshalJSON(data []byte) error {
	return engine.state.UnmarshalJSON(data)
}
func (engine *DockerTaskEngine) UnmarshalJSON(data []byte) error {
	return engine.state.UnmarshalJSON(data)
}
// UnmarshalJSON restores a previously marshaled task-engine state from json