setting ANSIBLE_PYTHON_INTERPRETER to auto will use the value from the
ansible/config/base.yml
debian is not included for this release of ansible but it whould work
for centos 6,7,8 and also for ubuntu 18,20.
Patch also removes pre-gate cleanup tasks for the new plain CI images[1]
[1] http://lists.openstack.org/pipermail/openstack-discuss/2020-May/015157.html
Co-Authored-By: Jonathan Rosser <jonathan.rosser@rd.bbc.co.uk>
Change-Id: I228ac8f4e02f0d344f524e093433414290ecb67f