Allow bypassing the logging setup via the Python API

[gaborbernat]

Resolves #1896.

[codecov]

Codecov Report

Merging #1904 into master will decrease coverage by 0.11%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1904      +/-   ##
==========================================
- Coverage   93.98%   93.86%   -0.12%     
==========================================
  Files          86       86              
  Lines        4220     4222       +2     
==========================================
- Hits         3966     3963       -3     
- Misses        254      259       +5     

Flag	Coverage Δ
#tests	93.86% <100.00%> (-0.12%)	⬇️

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Impacted Files	Coverage Δ
src/virtualenv/__init__.py	100.00% <100.00%> (ø)
src/virtualenv/run/__init__.py	95.77% <100.00%> (+0.12%)	⬆️
src/virtualenv/util/path/_sync.py	89.65% <0.00%> (-3.45%)	⬇️
src/virtualenv/seed/embed/base_embed.py	96.22% <0.00%> (-1.89%)	⬇️
src/virtualenv/util/subprocess/_win_subprocess.py	93.44% <0.00%> (-1.64%)	⬇️
src/virtualenv/create/creator.py	95.27% <0.00%> (-0.79%)	⬇️

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