Allow tools/test_history.py to be piped to head (#59676)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/59676
Test Plan:
```
tools/test_history.py --mode=columns --ref=3cf783 --test=test_set_dir --job pytorch_linux_xenial_py3_6_gcc5_4_test --job pytorch_linux_xenial_py3_6_gcc7_test | head -n10
```
Before this PR, the above command seems to just hang. After this PR, it nicely prints the following, line by line, and then exits:
```
2021-02-10 12:18:50Z 3cf78395cbc32fa9c83b585c9ec63f960b32d17f 0.644s 0.312s
2021-02-10 11:13:34Z 594a66d778a660faed0b0fbbe1dd8c2c318707ff 0.360s errored
2021-02-10 10:13:25Z 9c0caf0384690cb67dcccb7066ece5184f72ca78 0.819s 0.449s
2021-02-10 10:09:14Z 602434bcbebb82c6f3741b2a3d5ebac7ee482268 0.361s 0.454s
2021-02-10 10:09:10Z 2e35fe953553247d8a22fc38b039374e426f13b8
2021-02-10 10:09:07Z ff73be7e45616fe106b9e5040bc091ca5cdbfc7f
2021-02-10 10:05:39Z 74082f0d6f8dfd60f28c0de0fe43bcb97b95ee5a
2021-02-10 07:42:29Z 0620c96fd6a140e68c49d68ed14721b1ee108ecc 0.414s 0.377s (2 job re-runs omitted)
2021-02-10 07:27:53Z 33afb5f19f4e427f099653139ae45b661b8bc596 0.381s 0.294s
2021-02-10 07:05:15Z 5f9fb93c1423814a20007faa506ceb8b4828c8d1 0.461s 0.361s
```
Reviewed By: seemethere
Differential Revision: D28978017
Pulled By: samestep
fbshipit-source-id: 021e634bbf40eb1d3b131fac574343dd5cef5deb
