only load one direction generator in GPU

[JamesChenChina]

As mentioned in https://github.com/junyanz/pytorch-CycleGAN-and-pix2pix/blob/master/docs/qa.md, for pytorch version there is an option named --model_suffix which can load only one generator to produce the results in a single direction. This greatly saves GPU memory as we are not loading the discriminators and the other generator in the opposite direction.
Is there similar option in torch version that can save GPU memory when testing?

[junyanz]

We have implemented a similar model one_direction_test_model.