Issue 40055: test___all__ and test_distutils alters the enviroinment: pkg_resources.PEP440Warning

Even when no test is run, test_distutils alters the environment:

$ ./python -m test -v --fail-env-changed test_distutils -m DONTEXISTS
== CPython 3.7.7+ (heads/3.7:1cdc61c767, Mar 24 2020, 17:25:30) [GCC 9.2.1 20190827 (Red Hat 9.2.1-1)]
== Linux-5.5.9-200.fc31.x86_64-x86_64-with-fedora-31-Thirty_One little-endian
== cwd: /home/vstinner/python/3.7/build/test_python_157151
== CPU count: 8
== encodings: locale=UTF-8, FS=utf-8
0:00:00 load avg: 0.37 Run tests sequentially
0:00:00 load avg: 0.37 [1/1] test_distutils

----------------------------------------------------------------------

Ran 0 tests in 0.001s

OK
Warning -- warnings.filters was modified by test_distutils
  Before: (140048876788832, [], [])
  After:  (140048876788832, [], [('ignore', None, <class 'pkg_resources.PEP440Warning'>, None, 0)]) 
test_distutils run no tests

== Tests result: NO TEST RUN ==

1 test run no tests:
    test_distutils

Total duration: 655 ms
Tests result: NO TEST RUN


The problem comes from Lib/distutils/tests/test_check.py: "from distutils.command.check import check, HAS_DOCUTILS" imports indirectly the docutils module which imports pkg_resources.

pkg_resources changes warnings filters.


docutils is installed by python3-docutils-0.15.2-1.fc31.noarch package and pkg_resources comes from python3-setuptools-41.6.0-1.fc31.noarch package.


Attached PR disables docutils to avoid side effects of "import docutils" like pkg_resources modifying warnings filters.

> pkg_resources comes from python3-setuptools-41.6.0-1.fc31.noarch package.

Here is the line which alters warnings filters:

$ grep warnings /usr/lib/python3.7/site-packages/pkg_resources/__init__.py
(...)
warnings.filterwarnings("ignore", category=PEP440Warning, append=True)

New changeset 6e57237faf0da8904e0130a11350cae3c5062b82 by Victor Stinner in branch 'master':
bpo-40055: test_distutils leaves warnings filters unchanged (GH-20095)
https://github.com/python/cpython/commit/6e57237faf0da8904e0130a11350cae3c5062b82

New changeset 7ef275160953f00b4303149df6d919c0afe763cb by Miss Islington (bot) in branch '3.7':
bpo-40055: test_distutils leaves warnings filters unchanged (GH-20095)
https://github.com/python/cpython/commit/7ef275160953f00b4303149df6d919c0afe763cb

New changeset 4e6545b002dd4d068b2538ffca60830d0e7fd369 by Miss Islington (bot) in branch '3.8':
bpo-40055: test_distutils leaves warnings filters unchanged (GH-20095)
https://github.com/python/cpython/commit/4e6545b002dd4d068b2538ffca60830d0e7fd369