Add pylint and flake8 tests to GitLab CI

Our python code didn't adhere to any coding standard.  In this commit, we add
flame8 (https://pypi.org/project/flake8/), and pylint (https://www.pylint.org/).

There's couple of exceptions:

- ans.py scripts are not checked, nor fixed as part of this MR
- pylint's missing-*-docstring and duplicate-code checks have
  been disabled via .pylintrc

Both exceptions should be removed in due time.

.gitlab-ci.yml

@@ -418,6 +418,37 @@ coccinelle:
     - util/check-cocci
     - if test "$(git status --porcelain | grep -Ev '\?\?' | wc -l)" -gt "0"; then git status --short; exit 1; fi
 
+flake8:
+  <<: *default_triggering_rules
+  <<: *base_image
+  stage: postcheck
+  needs:
+    - job: autoreconf
+      artifacts: true
+  before_script:
+    - pip3 install flake8
+  script:
+    - *configure
+    - flake8 --max-line-length=80 $(git ls-files '*.py' | grep -v 'ans\.py')
+  only:
+    - merge_requests
+
+pylint:
+  <<: *default_triggering_rules
+  <<: *base_image
+  stage: postcheck
+  needs:
+    - job: autoreconf
+      artifacts: true
+  before_script:
+    - pip3 install pylint
+    - PYTHONPATH="$PYTHONPATH:$CI_PROJECT_DIR/bin/python"
+  script:
+    - *configure
+    - pylint --rcfile $CI_PROJECT_DIR/.pylintrc $(git ls-files '*.py' | grep -v 'ans\.py')
+  only:
+    - merge_requests
+
 tarball-create:
   stage: precheck
   <<: *base_image

.pylintrc

@@ -0,0 +1,6 @@
+[MASTER]
+disable=
+    C0114, # missing-module-docstring
+    C0115, # missing-class-docstring
+    C0116, # missing-function-docstring
+    R0801, # duplicate-code

util/copyrights

@@ -1,4 +1,5 @@
 ./.gitlab-ci.yml				X	2018,2019,2020
+./.pylintrc					X	2020
 ./.uncrustify.cfg				X	2018,2019,2020
 ./CHANGES					X	2000,2001,2002,2003,2004,2005,2006,2007,2008,2009,2010,2011,2012,2013,2014,2015,2016,2017,2018,2019,2020
 ./CODE_OF_CONDUCT				X	2019,2020