If no public API network is used, as in the case of typical all-in-one
environments, the checks in kolla-ansible.yml, task "Validate Kolla
Ansible API address configuration" may fail. This happens only when
using the new kolla_internal_vip_address variable, and not if the legacy
vip_address network attribute is used.

This change fixes the issue by only checking for valid external VIP
address/FQDN configuration when a separate public API network is in use.
If the external VIP/FQDN are not set, then Kayobe no longer defaults
their values to the internal VIP/FQDN, instead relying on the Kolla
Ansible defaults to do this. This may have consequences for anyone
relying on these variables in configuration.

Change-Id: I0b1c963006c044ade5c67c4046da5e2addc9a8c7
Story: 2009134
Task: 43070