Fixing pylint failures in zuul.

pylint running in python3.8 will complain about some
code such as 'import contextlib'

Rather than destabilize the code, specify python3.6 for
the pylint job.

When python2 is fully dropped, the changes can be addressed.

The zuul nodeset for bionic sets up a venv for python3.6

Closes-Bug: #1928841
Signed-off-by: albailey <Al.Bailey@windriver.com>
Change-Id: Ib2e7f467ce20e5b31aef7242405ef034583d4e1a

.zuul.yaml

@@ -88,6 +88,7 @@
     parent: tox
     description: |
       Run pylint test for sysinv
+    nodeset: ubuntu-bionic
     required-projects:
       - starlingx/fault
       - starlingx/update

sysinv/sysinv/sysinv/sysinv/helm/common.py

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2018-2020 Wind River Systems, Inc.
+# Copyright (c) 2018-2021 Wind River Systems, Inc.
 #
 # SPDX-License-Identifier: Apache-2.0
 #

sysinv/sysinv/sysinv/tox.ini

@@ -164,7 +164,7 @@ deps = -r{toxinidir}/test-requirements.txt
 commands = bandit --ini tox.ini -n 5 -r sysinv
 
 [testenv:pylint]
-basepython = python3
+basepython = python3.6
 commands =
      pylint {posargs} sysinv --rcfile=./pylint.rc