Fix Torch-TRT backend and userbenchmark (#1957)
Summary:
- Improve error checking in benchmark
- Improve argument handling and processing in backend
Pull Request resolved: https://github.com/pytorch/benchmark/pull/1957
Reviewed By: aaronenyeshi
Differential Revision: D49912033
Pulled By: xuzhao9
fbshipit-source-id: 8709e738344885b7af6619ca13f437b67ef380dd
