Refactor randperm test (#23526)
Summary:
CPU and CUDA testing code are largely the same.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23526
Reviewed By: ezyang
Differential Revision: D16586271
Pulled By: VitalyFedyunin
fbshipit-source-id: 91c70c05789120fde4718ce955de243087a8c993
