Add `--stress` option to `run.py` (#1002)
Summary:
Add `--stress <seconds>` option to `run.py`. Users can specify a number of minutes to stress devices.
Related to Issue https://github.com/pytorch/benchmark/issues/904
Pull Request resolved: https://github.com/pytorch/benchmark/pull/1002
Reviewed By: xuzhao9
Differential Revision: D37506403
Pulled By: FindHao
fbshipit-source-id: cc4d39a61953957d4be3cc219c41b1e63f096ee1
