Issue 35458: test_shutil.test_disk_usage() randomly fails when tests are run in parallel

Extract of the test:

        usage = shutil.disk_usage(os.path.dirname(__file__))
        self.assertEqual(usage, shutil.disk_usage(__file__))

The test fails if another process creates or removes data on the disk partition. IMHO "self.assertEqual(usage, shutil.disk_usage(__file__))" must be removed, it cannot be reliable without mocking os.statvfs() / nt._getdiskusage().

Even if tests are run sequentially, the test can fail if a program creates a file between the two lines of code, the test cannot be reliable.

https://buildbot.python.org/all/#/builders/85/builds/1882

FAIL: test_disk_usage (test.test_shutil.TestShutil)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/shager/cpython-buildarea/3.x.edelsohn-fedora-ppc64le/build/Lib/test/test_shutil.py", line 1366, in test_disk_usage
    self.assertEqual(usage, shutil.disk_usage(__file__))
AssertionError: usage(total=1925696024576, used=1793793806336, free=131902218240) != usage(total=1925696024576, used=1793793818624, free=131902205952)

The new test has been added by PR 9372:

commit c8c0249c9e8f61ab7670119a5a5278354df27bbb
Author: Joe Pamer <jopamer@users.noreply.github.com>
Date:   Tue Sep 25 10:57:36 2018 -0400

    bpo-32557: allow shutil.disk_usage to take a file path on Windows also (GH-9372)

Only the master branch is impacted (see bpo-32557).

New changeset dc525f4315cdbe84693396d3f7a65a00425743bb by Victor Stinner in branch 'master':
bpo-35458: Fix test_shutil.test_disk_usage() (GH-11111)
https://github.com/python/cpython/commit/dc525f4315cdbe84693396d3f7a65a00425743bb