pipelines: add lint-py to linter pipeline

[refack]

fixes: #1631

example output (master):

18:38:04  + python tools/getnodeversion.py
18:38:05  [Pipeline] sh
18:38:09  + NODE=node PYTHON=python3 gmake lint-py
18:38:09  PYTHONPATH=tools/pip python3 -m flake8 . \
18:38:09  	--count --show-source --statistics --select=E901,E999,F821,F822,F823 \
18:38:09  	--exclude=.git,deps,lib,src,test/fixtures,tools/*_macros.py,tools/gyp,tools/inspector_protocol,tools/jinja2,tools/markupsafe,tools/pip
18:38:18  0
18:38:19  [Pipeline] sh
18:38:22  + NODE=node gmake lint-ci
18:38:22  Running JS linter...
18:39:43  Running C++ linter...
18:40:19  PYTHONPATH=tools/pip python -m flake8 . \
18:40:19  	--count --show-source --statistics --select=E901,E999,F821,F822,F823 \
18:40:19  	--exclude=.git,deps,lib,src,test/fixtures,tools/*_macros.py,tools/gyp,tools/inspector_protocol,tools/jinja2,tools/markupsafe,tools/pip
18:40:25  0

v10.x-staging:

18:43:20  + python tools/getnodeversion.py
18:43:20  [Pipeline] sh
18:43:22  + NODE=node gmake lint-ci

v8.x-staging - https://ci.nodejs.org/job/node-linter/3040/console

19:19:36  + python tools/getnodeversion.py
19:19:37  [Pipeline] echo
19:19:37  8.15.2
19:19:37  [Pipeline] sh
19:19:38  + NODE=node gmake lint-ci
19:19:38  Running JS linter...
19:20:19  Running C++ linter on addon docs...

[richardlau]

Oh and you've mispelled linter in the commit message and PR title 😆.

[refack]

New CI for master - https://ci.nodejs.org/job/node-linter/3048/console
New CI for v8.x - https://ci.nodejs.org/job/node-linter/3049/console

[refack]

v6.x Linter: https://ci.nodejs.org/job/node-linter/3116/ ✔️
v6.x Lite-CI: https://ci.nodejs.org/job/node-test-pull-request-lite-pipeline/3146/ ✔️

[Trott]

/ping @nodejs/jenkins-admins to see if anyone else wants to take a look at this

[cclauss]

This is linting on both Python 2 and 3?

[richardlau]

This is linting on both Python 2 and 3?

Yes for versions of Node.js > 11.

[sam-github]

@richardlau do you understand enough to land this, or call it stale and close it?

[richardlau]

These changes have already been made to the pipelines in question* so this PR is basically merging those changes to the backup jenkinsfile in this repository. We can have a separate discussion about whether having jenkinsfiles in SCM and not using those directly in the Jenkins jobs is a good idea or not but for now I'll just merge this in so the files here matches the scripts in the jobs.

* We haven't been running the node-test-pull-request-lite-pipeline job since we allowed just Travis CI for doc-only changes. I think there were reports over the Christmas period that it's possibly broken. Maybe we should just remove it? (Linting is done in node-test-pull-request/node-test-commit by a different lint job in Jenkins and we're also running the linters on Travis CI and GitHub Actions so it's not as if we're lacking coverage here.)