italy_yaml: fix loading of OutputOnly tasks (and some drive-by cleanups)

[prandla]

• loading of OutputOnly tasks with italy_yaml was broken, because the part that set OutputOnly was overwritten by a later if statement.
• Changed the "communication NAND interactive" check to also take outputonly into account, and made that check actually terminate the process instead of just continuing anyways.
• I also did a small cleanup (replace logging.fatal with logging.critical, since the former's docstring says "Don't use this function, use critical() instead.") and I removed some python 2 compat code.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 11 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.72%. Comparing base (06caa18) to head (9907de1).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cmscontrib/loaders/italy_yaml.py	0.00%	11 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1723      +/-   ##
==========================================
- Coverage   56.72%   56.72%   -0.01%     
==========================================
  Files         344      344              
  Lines       28310    28308       -2     
==========================================
- Hits        16059    16057       -2     
  Misses      12251    12251              

Flag	Coverage Δ
functionaltests	0.00% <0.00%> (ø)
unittests	56.72% <0.00%> (-0.01%)	⬇️

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