Until now, the inventory path used by the overcloud_delete.py was wrong,
since it wasn't using the "stackname", leading to a wrong
/home/stack/config-download/{}/tripleo-ansible-inventory.yaml path.
While it's not a big issue with non-TLS-e deploy, it becomes an actual
problem when we involve FreeIPA and TLS-e, since the deletion won't
remove the nodes nor services from FreeIPA.
Closes-Bug: #1950155
Change-Id: I5941bf9948c5f17e7406d34c21b8de9bd174c063