I was able to get PyTorch working on the V100 instances on AWS as well. I have my own Packer based script 37 to package/customize an AMI using anaconda python  where the following script handles the GPU stuff https://github.com/Pinafore/qb/blob/master/packer/bin/install-cuda.sh 51.
That was written for CUDA 8, so I started with an instance using that image, and then installed CUDA 9 plus compatible versions of cuDNN and NCCL. After that I was able to do a simple python setup.py install from the current master branch then start using PyTorch normally.