Description of problem:
The OPENSTACK_KEYSTONE_DOMAIN_DROPDOWN and OPENSTACK_KEYSTONE_DOMAIN_CHOICES options were added to Horizon in the OpenStack Pike release. However the keystone_domain_choices puppet parameter which allows setting these options via Director/TripleO was not added to puppet-horizon until the Rocky release.
This should be backported to the Red Hat supported Queens release (OSP13) to align with the Horizon update.
Version-Release number of selected component (if applicable):
Steps to Reproduce: