Add abtest script for userbenchmark PR testing (#936)
Summary:
This PR adds script to support running userbenchmark in TorchBench PR testing.
Pull Request resolved: https://github.com/pytorch/benchmark/pull/936
Test Plan:
```
$ python ./.github/scripts/abtest.py --pytorch-repo $HOME/srcs/pytorch --base 308d813 --head 308d813 --userbenchmark nvfuser --output-dir $PWD --skip-build
Metric;2d5eac48d5;2d5eac48d5
nnc-dynamic:autogen-0;0.030607475398574023;0.029107386199757456
nnc-dynamic:autogen-1;0.018465964397182687;0.01845656605437398
nnc-dynamic:autogen-10;0.015184402704471722;0.015656903700437395
nnc-dynamic:autogen-11;0.018875993497204036;0.01948478349368088
nnc-dynamic:autogen-12;0.02349025229923427;0.023829517804551868
nnc-dynamic:autogen-13;0.34809359710197896;0.34824983193539083
nnc-dynamic:autogen-14;1.3703643198823556;1.3697424699785188
nnc-dynamic:autogen-15;0.0198644844465889;0.021008694299962372
nnc-dynamic:autogen-16;0.04262202540412545;0.04256983210798353
nnc-dynamic:autogen-17;0.19357904349453747;0.19364229351049286
nnc-dynamic:autogen-18;0.029893740301486105;0.030662423500325532
nnc-dynamic:autogen-19;0.031198418303392827;0.03185724349459633
...
```
Reviewed By: davidberard98
Differential Revision: D36799962
Pulled By: xuzhao9
fbshipit-source-id: 80c9ba2179603a5b021793146c82f828c7af78c8
