octavia: Ensure service auth project exists

Kolla Ansible supports configuration of the project used by Octavia to
communicate with other services, via octavia_service_auth_project. Until
Ussuri, this was set to admin. In Ussuri it changed to service. It may
also be set to a different value.

Kolla Ansible currently gives the octavia user the admin role in the
project, but it does not ensure that the project exists. For admin and
service projects, this is not a problem. If the project has been
customised however, it will not necessarily exist, which will cause
Octavia deployment to fail.

This change fixes the issue by ensuring that the service auth project
exists, in addition to the service project.

Closes-Bug: #1922100
Change-Id: I968efbf3ad1de676548b4e3aeefc20bf80ca94a0