change shape for some ops to reduce variance
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/25619
Test Plan:
```
[huaminli@devvm2388.ftw3 ~/fbsource/fbcode] buck run mode/dev-nosan caffe2/benchmarks/operator_benchmark:benchmark_all_test -- --operators None --iterations 3
```
last few lines of output P108286305
Reviewed By: mingzhe09088
Differential Revision: D17175802
fbshipit-source-id: 46b69fc1895444b15b6dfcec0625b6b9b006712a
