Upgrade virtualenv in pre

Since virtualenv 20.0 (amongst other changes) six version >1.12.0 is required.
This change adds upgrade of virtualenv and six in pre - to be reverted once
infra CentOS images are sorted out.

Depends-On: https://review.opendev.org/707377
Change-Id: I75249055989309d0afdfc29c894beb6b1fcd1994

tests/playbooks/pre.yml

@@ -3,6 +3,11 @@
   roles:
     - bindep
   tasks:
+    # TODO(mnasiadka): Remove once infra merges virtualenv fixes
+    - name: Upgrade virtualenv package
+      command: python3 -m pip install -U virtualenv
+      become: True
+
     - name: Create dir for kolla logs
       file:
         path: "{{ kolla_logs_dir }}"