Python 3.8 collections compatibility fixes.

Includes a new pylint blacklist plugin to prevent regressions.

test/units/modules/conftest.py

@@ -2,12 +2,12 @@
 # GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
 
 import json
-from collections import MutableMapping
 
 import pytest
 
 from ansible.module_utils.six import string_types
 from ansible.module_utils._text import to_bytes
+from ansible.module_utils.common._collections_compat import MutableMapping
 
 
 @pytest.fixture