Added some extra tests for std_mean and var_mean for multiple dims. (#20650)
Summary:
Added some extra tests for std_mean and var_mean for multiple dims.
Some refactoring of previously created tests based on PR comments: https://github.com/pytorch/pytorch/pull/18731
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20650
Differential Revision: D15396101
Pulled By: ifedan
fbshipit-source-id: d15c3c2c7084a24d6cfea4018173552fcc9c03a9
