Don't test with setuptools local distutils.

We noticed some aberrations in log level/threshold handling as of
Setuptools 60.0.0, and the only substantive change for that release[1]
toggles the default selection for its internal ("local") distutils
replacement vs the "stdlib" one. For now, toggle the
SETUPTOOLS_USE_DISTUTILS envvar in our testing back to the old
value. This should be revisited once logging is handled better in
Setuptools.

[1] pypa/setuptools#3038

Change-Id: I2eacb9756d9eb9c5d606599f16cdb412007f5854

tox.ini

@@ -5,6 +5,10 @@ ignore_basepython_conflict = true
 
 [testenv]
 basepython = python3
+# TODO(damani): Drop distutils override once logging improves in setuptools
+#              https://github.com/pypa/setuptools/issues/3038
+setenv =
+  SETUPTOOLS_USE_DISTUTILS=stdlib
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
   -r{toxinidir}/test-requirements.txt
@@ -30,7 +34,10 @@ commands =
   sphinx-build -W --keep-going -b html doc/source doc/build/html
 
 [testenv:cover]
+# TODO(damani): Drop distutils override once logging improves in setuptools
+#              https://github.com/pypa/setuptools/issues/3038
 setenv =
+  SETUPTOOLS_USE_DISTUTILS=stdlib
   PYTHON=coverage run --source oslo_context --parallel-mode
 commands =
   stestr run {posargs}