In order to migrate to use of PKI role for Octavia,
we need to feed already existing certificates to the PKI role. For that
we're creating an overrides file, that will define already existing
certificates like they are user-provided ones.
Needed-By: https://review.opendev.org/c/openstack/openstack-ansible-os_octavia/+/839068
Change-Id: I848a453a3c0240fa2da5b51d1f088e87ba0888d4