[CI] Let Tenks manage its own venv

This way it works closer to what Tenks does in its own CI.

See-also: https://review.opendev.org/c/openstack/tenks/+/856296
Change-Id: I5bebcb3520aada3abc8b7d0d4087e7a3f9277df2

tests/run.yml

@@ -455,7 +455,10 @@
                 executable: /bin/bash
                 chdir: "{{ kolla_ansible_src_dir }}"
               environment:
-                TENKS_VENV_PATH: "{{ ansible_env.HOME }}/tenks-venv"
+                # NOTE(yoctozepto): This is kolla-ansible-tenks-venv to avoid
+                # a conflict with the venv that Tenks creates by itself
+                # by default to ~/tenks-venv
+                TENKS_VENV_PATH: "{{ ansible_env.HOME }}/kolla-ansible-tenks-venv"
                 TENKS_SRC_PATH: "{{ ansible_env.HOME }}/src/opendev.org/openstack/tenks"
 
             - name: Run test-ironic.sh script