[test] Improved tests to avoid all-breaking asserts and inter-test messup

[ethouris]

1. Some small refax in api.cpp (shortcut variables, preparing for another change)
2. Added possibly handling -lognote option and added handling in FileUpload test.
3. Reworked test_reuseaddr.cpp to use a fixture and a propoer resource management.
4. Added similar fixes in other tests.

[codecov]

Codecov Report

Attention: Patch coverage is 83.41969% with 32 lines in your changes are missing coverage. Please review.

Project coverage is 65.01%. Comparing base (04acbba) to head (ca98ee3).

Files	Patch %	Lines
test/test_reuseaddr.cpp	84.13%	23 Missing ⚠️
srtcore/api.cpp	50.00%	5 Missing ⚠️
test/test_file_transmission.cpp	80.00%	2 Missing ⚠️
test/test_main.cpp	80.00%	1 Missing ⚠️
test/test_many_connections.cpp	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2892      +/-   ##
==========================================
+ Coverage   64.84%   65.01%   +0.16%     
==========================================
  Files         101      101              
  Lines       17536    17544       +8     
==========================================
+ Hits        11372    11407      +35     
+ Misses       6164     6137      -27     

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