Venv for kolla-ansible does not respect selected python

[DavidFair]

Setting a custom Python version (e.g. python3.10) on Beokay does not set the environment up correctly for the kayobe-ansible virtual environment, instead using the system default python3 rather than the specified version to Beokay

There's a couple of missing pieces from Beokay's side to make this work:

• We don't create a venv for kolla-ansible so the playbook has to guess, if we created it with the right version and set the env Kolla would do the correct thing
• Alternatively, we could pass the user's selected Python version along to the playbook using kolla_ansible_venv or a similar var to let Kolla do the lifting

Currently a user will get mismatched environments in venv, one pointing to their selected Python the other pointing to the OS Python.