How to parse any arch in NAS-Bench-101 as pytorch class to train.

Hi,
I'm trying to sample few architectures from NAS-Bench-101, and then query the socre, and also get the torch-model according to the architecutre.

I wanna use the model to do some customer training or testing.

In core/graph.py, it shows we should us the following code to parse the model to pytorch module

```
**Use as pytorch module**
If you want to learn the weights of the operations or any
other parameters of the graph you have to parse it first.
>>> graph = getFancySearchSpace()
>>> graph.parse()
>>> logits = graph(data)
>>> optimizer.min(loss(logits, target))
```

But the graph.parse() will fail if i use NasBench101SearchSpace as graph instance ,