run-tests: fix a crash when using the coverage options

35bf7f23b84c attempted to transition away from `distutils`, but the `packaging`
code lacks `StrictVersion`.  I have no idea when `packaging.version` became
available, but I have it in python 3.6, so that should be good enough.  For some
reason, the import checker thinks this is a local import, and needs help to
decide otherwise.

Alternately we could ditch the version check entirely, because `coverage` is
currently at 7.2.1, and the original check was added back in 2010.

contrib/import-checker.py

@@ -232,6 +232,7 b' def list_stdlib_modules():'
     yield 'importlib.abc'  # python3 only
     yield 'importlib.machinery'  # python3 only
     yield 'importlib.util'  # python3 only
+    yield 'packaging.version'
     for m in 'fcntl', 'grp', 'pwd', 'termios':  # Unix only
         yield m
     for m in 'cPickle', 'datetime':  # in Python (not C) on PyPy

tests/run-tests.py

@@ -54,6 +54,7 b' import functools'
 import json
 import multiprocessing
 import os
+import packaging.version as version
 import platform
 import queue
 import random
@@ -72,12 +73,6 b' import unittest'
 import uuid
 import xml.dom.minidom as minidom
 
-try:
-    # PEP 632 recommend the use of `packaging.version` to replace the
-    # deprecated `distutil.version`. So lets do it.
-    import packaging.version as version
-except ImportError:
-    import distutils.version as version
 
 if sys.version_info < (3, 5, 0):
     print(
@@ -799,8 +794,8 b' def parseargs(args, parser):'
         try:
             import coverage
 
-            covver = version.StrictVersion(coverage.__version__).version
-            if covver < (3, 3):
+            covver = version.Version(coverage.__version__)
+            if covver < version.Version("3.3"):
                 parser.error('coverage options require coverage 3.3 or later')
         except ImportError:
             parser.error('coverage options now require the coverage package')