allow passing a list of operators to benchmark (#23442)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23442
Replace the argument name from `operator` to `operators` which can take a list of operators to test.
Reviewed By: hl475
Differential Revision: D16520779
fbshipit-source-id: 94284a87c64471793e319f5bd3143f89b9a192bb
