Fix JSON file format Torch-TRT (#1998)
Summary:
- Remove error message strings in JSON, opting for -1.0 as the error code instead
- Add support for graph breaks metric in benchmark JSON
- A future PR will add separate `.txt` files for each erroring model
Pull Request resolved: https://github.com/pytorch/benchmark/pull/1998
Reviewed By: aaronenyeshi
Differential Revision: D50511826
Pulled By: xuzhao9
fbshipit-source-id: acea66441d834d69f31713b4e293902dd0106c5a
