Summary:
Another small refactor trying to reduce non-trivial logic existing
inside the `tools` scripts. I considered moving `main` as
`run_inference_and_check_expected_results` but that just sounded uglier.

Reviewed By: rbgirshick

Differential Revision: D7432976

fbshipit-source-id: a31106e11cf0c1d93781fc9a696d2afee553f3d6