judge: clarify short-circuit behaviour and test short circuit

[Riolku]

The previous code was a bit hard to follow.

[Riolku]

I think actually it's worth making some good tests for this PR as well. I'll re-open when I do that.

[codecov-commenter]

Codecov Report

Merging #1022 (e555ec6) into master (9551b06) will decrease coverage by 27.92%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           master    #1022       +/-   ##
===========================================
- Coverage   81.24%   53.32%   -27.93%     
===========================================
  Files         140      140               
  Lines        4789     4786        -3     
===========================================
- Hits         3891     2552     -1339     
- Misses        898     2234     +1336     

Impacted Files	Coverage Δ
dmoj/judge.py	25.00% <100.00%> (-27.77%)	:arrow_down:
dmoj/executors/C.py	0.00% <0.00%> (-100.00%)	:arrow_down:
dmoj/executors/D.py	0.00% <0.00%> (-100.00%)	:arrow_down:
dmoj/executors/GO.py	0.00% <0.00%> (-100.00%)	:arrow_down:
dmoj/executors/ADA.py	0.00% <0.00%> (-100.00%)	:arrow_down:
dmoj/executors/AWK.py	0.00% <0.00%> (-100.00%)	:arrow_down:
dmoj/executors/C11.py	0.00% <0.00%> (-100.00%)	:arrow_down:
dmoj/executors/F95.py	0.00% <0.00%> (-100.00%)	:arrow_down:
dmoj/executors/ICK.py	0.00% <0.00%> (-100.00%)	:arrow_down:
dmoj/executors/LUA.py	0.00% <0.00%> (-100.00%)	:arrow_down:
... and 85 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more Δ = absolute <relative> (impact), ø = not affected, ? = missing data Powered by Codecov. Last update 9551b06...e555ec6. Read the comment docs.

[Riolku]

Now tests global shortcircuit and pretest shortcircuit explicitly.

[Xyene]

Closing since this is superseded by https://github.com/DMOJ/judge-server/pull/1075, feel free to reopen if you disagree.