Set two different image in tempest irespective of DEFAULT_IMAGE_NAME

In current logic to set two different image in Tempest in config
option image_ref and image_ref_alt, we consider if DEFAULT_IMAGE_NAME
is found in glance then set the same image in tempest for those
two config option. This means even we have two different image available
in glance, still we set same image in image_ref as well as image_ref_alt
and all the rebuild tests are rebuilt on the same image.

I could not find any reason why we set same image if DEFAULT_IMAGE_NAME
exist, below are the original change added this logic
- https://review.opendev.org/c/openstack/devstack/+/17553

We had a requirement of test to run on two different images
- https://review.opendev.org/c/openstack/tempest/+/831018

and for that we need to set DEFAULT_IMAGE_NAME to non exist image
name but that broke the Ironic which was reply on the valid name
in DEFAULT_IMAGE_NAME
- https://review.opendev.org/c/openstack/ironic/+/886790

As we do not have any reason not to set two different image
if DEFAULT_IMAGE_NAME is set, I am removing the condition of
DEFAULT_IMAGE_NAME from lib/tempest logic and always set two
different images if they are available.

Depends-On: https://review.opendev.org/c/openstack/tempest/+/886796

Change-Id: I9d215f48d4440f2fa6dcc0d222a10896caf01215
1 file changed