automate sharding using S3 test time stats (#53269)
Summary:
Uses nightly commit stats to automatically shard tests based on execution time.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/53269
Test Plan:
set CIRCLE_JOB to an existing job, like `pytorch_linux_bionic_py3_6_clang9_test`
Then you can run something like: `python test/run_test.py --shard 1 10`
Reviewed By: malfet
Differential Revision: D26819440
Pulled By: janeyx99
fbshipit-source-id: 6bc73d6aa3d52d9850817536be15d7b54a72780e
