Correct how we fetch External and InternalApi networks name
Correct how we fetch External and InternalApi networks name

Change[1] moved away from yaql, making things easier to read and debug.
This patch corrects a small issue, where the "external_net_name" and
"internal_api_net_name" wouldn't be set in case we're using some custom
name in a network plan.

[1] https://review.opendev.org/666447

Change-Id: I1a385bca9fd4a8712f27a8a42617b6f3023971b4
Co-Authored-By: James Slagle <33ab48cedd1a7cf7a68e1b587db88f55f753652f@redhat.com>

openstack/tripleo-common,openstack/tripleo-common