Fix misc issues regarding user tests with graders

[ranaldmiao]

• This PR primarily fixes the issue described in User testing does not pick up header files #1153 where header files cannot be found for user tests

This implementation re-uses the same header files as that for actual submissions. (Assumption: Task authors typically do not have different implementations for public and private header files.)

• This PR also allows for graders for user tests to be downloaded. Previously, a HTTP 404 will be encountered when contestants select the option to download grader files from their user tests.

It seems that graders are not stored with the .%l suffix (Eg: grader.%l) but the original extension (Eg: grader.cpp) instead. Hence, this PR introduces an additional check for the original filename before declaring HTTP 404.

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This change is 

[codecov]

Codecov Report

Merging #1172 (0e34b78) into master (9236084) will decrease coverage by 0.13%.
The diff coverage is 33.33%.

@@            Coverage Diff             @@
##           master    #1172      +/-   ##
==========================================
- Coverage   63.63%   63.50%   -0.14%     
==========================================
  Files         232      232              
  Lines       17044    17048       +4     
==========================================
- Hits        10846    10826      -20     
- Misses       6198     6222      +24     

Flag	Coverage Δ
functionaltests	47.42% <33.33%> (-0.15%)	⬇️
unittests	44.13% <0.00%> (-0.02%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
cms/server/contest/handlers/taskusertest.py	46.55% <0.00%> (ø)
cms/grading/Job.py	89.73% <50.00%> (-0.73%)	⬇️
cms/service/EvaluationService.py	71.39% <0.00%> (-2.74%)	⬇️
cms/server/contest/handlers/tasksubmission.py	48.63% <0.00%> (-2.19%)	⬇️
cms/db/base.py	87.12% <0.00%> (-1.99%)	⬇️
cms/service/esoperations.py	79.86% <0.00%> (-1.39%)	⬇️
cms/io/rpc.py	92.85% <0.00%> (-1.37%)	⬇️
cms/service/ProxyService.py	66.66% <0.00%> (-1.02%)	⬇️
cms/service/ResourceService.py	59.11% <0.00%> (-0.89%)	⬇️
cms/server/admin/handlers/base.py	70.29% <0.00%> (-0.67%)	⬇️
... and 5 more

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[andreyv]

Thanks for the fixes!

The first change is related to TaskType.get_auto_managers(), which is supposed to return managers to be taken from the task. But you can see that currently there is no way for get_auto_managers() to account for a non-mandatory, arbitrarily named .h manager (even less so for additional .o managers). One could make it work now by returning None instead of [] from Batch.get_auto_managers(), but I don't think this is intended.

So I think that for now the proposed change is a sufficient short-term fix until a general solution is worked out.

The second change looks good. Managers are in general stored without .%l in the database, so it is fitting to do the same here.

[ranaldmiao]

Thanks for the review, @andreyv

Made the requested changes.

[andreyv]

Thanks, merged. Also added tests in 81fb9df.