Roll role-addition jobs to python3 (centos-8)

This change moves our role-addition jobs to using centos-8 because
pre-commit has dropped support for python2 as noted here [0]. Due
to this dropped support, the role-addition job needs to be executed
on a system that has access to py3.

[0] https://github.com/ansible/ansible-lint/issues/683#issuecomment-592084930
Signed-off-by: Kevin Carter <kecarter@redhat.com>

Change-Id: Iec83c9a3510ef000272dae446346996242cadc8c

tox.ini

@@ -117,6 +117,7 @@ ignore = D001
 commands = {posargs}
 
 [testenv:role-addition]
+basepython = python3
 deps=
   {[testenv:linters]deps}
 commands =

zuul.d/molecule.yaml

@@ -42,7 +42,7 @@
       - tripleo-ansible-centos-7-molecule-tripleo_upgrade_hiera
       - tripleo-ansible-centos-7-molecule-tripleo_validations_package
       - tripleo-ansible-centos-7-molecule-tuned
-      - tripleo-ansible-centos-7-role-addition
+      - tripleo-ansible-centos-8-role-addition
     gate:
       jobs:
       - tripleo-ansible-centos-7-molecule-aide
@@ -85,7 +85,7 @@
       - tripleo-ansible-centos-7-molecule-tripleo_upgrade_hiera
       - tripleo-ansible-centos-7-molecule-tripleo_validations_package
       - tripleo-ansible-centos-7-molecule-tuned
-      - tripleo-ansible-centos-7-role-addition
+      - tripleo-ansible-centos-8-role-addition
     name: tripleo-ansible-molecule-jobs
 - job:
     files:
@@ -388,8 +388,8 @@
     - ^tox.ini
     - ^molecule-requirements.txt
     - ^zuul.d/playbooks/.*
-    name: tripleo-ansible-centos-7-role-addition
+    name: tripleo-ansible-centos-8-role-addition
-    nodeset: centos-7
+    nodeset: centos-8
     parent: tox-molecule
     timeout: 1800
     vars: