Drop horizon_keystone_host variable

The horizon_keystone_host is only used as interpolation
for OPENSTACK_KEYSTONE_URL, which we define manually. So
horizon_keystone_hosts server no purpose.

Change-Id: I693bdb30e3d812592f023c00fbbbd62f069320bf

defaults/main.yml

@@ -240,7 +240,6 @@ horizon_secure_proxy_ssl_header_django: "HTTP_{{ horizon_secure_proxy_ssl_header
 #   - { url: "http://cluster1.example.com:5000/v2.0", name: "RegionTwo" }
 
 ## Horizon's keystone endpoint settings
-horizon_keystone_host: "{{ internal_lb_vip_address }}"
 horizon_keystone_endpoint: "{{ keystone_service_internalurl }}"
 
 ## Horizon Multi-Domain Support

templates/horizon_local_settings.py.j2

@@ -178,9 +178,6 @@ AVAILABLE_REGIONS = [
   ('{{ item.url }}', '{{ item.name }}'),
 {% endfor %}
 ]
-{% else %}
-# Set Horizon to use a specific Keystone endpoint
-OPENSTACK_HOST = "{{ horizon_keystone_host }}"
 {% endif %}
 
 OPENSTACK_KEYSTONE_URL = "{{ horizon_keystone_endpoint }}"