Make sure octavia uses internal endpoint to barbican

The octavia service communicates to the barbican service with
public endpoint_type by default[1], it should use internal
like other services.

[1] https://github.com/openstack/octavia/blob/0056b5175f89070164849501ec6d960549b95e34/octavia/common/config.py#L533-L537

Closes-Bug: #1875618
Change-Id: I90d2b0aeac090a3e2366341e260232fc1f0d6492