build_aux: move the PyLint task from Jenkins to Zuul
How it was done:
https://fedoraproject.org/wiki/Zuul-based-ci
Previously, when the run was run against improperly rebased
pull-request, the differences between PR code and 'upstream/master'
branch were unnecessary big. That was because something got merged
upstream in the meantime, most likely _fixing_ some PyLint issues rather
then adding new. Such upstream-fixed PyLint issues previously poisoned
the output of the script, and appeared as "new" issues.
So why I am on this script, I implemented automatic rebase against
'upstream/master' branch first. If the rebase fails, the whole
pull-request requires manual rebase and fix conflicts. But if succeeds,
only the relevant issues should stay printed.
Merges: #1674
Replaces: #1671