Configure DB addresses for each service

To enable partitioning of DB traffic by-service, each service needs to
use a custom connection string. Defaulting the service address to a
common galera_address makes things continue to work by default.

While the galera_address could be overridden on a container or host
basis this requires repeating that behavior across each infra node in
the inventory. Providing service-specific connection address variables
simplifies the management somewhat for large deployments and may reduce
error rates.

The service install playbooks now default the service-specific variables
instead of galera_address to the internal lb vip from inventory to
maintain the ease-of-use currently available.

Any value for a service-specific variable set in user_variables.yml will
override the value in the playbook's vars to provide selective
customization as needed.

Change-Id: I4c98bf906a0c1cb11ddd41277a855dce22ff646a
Closes-Bug: 1462529

README.rst

@@ -16,4 +16,4 @@ This role will install the following:
       roles:
         - { role: "os_horizon", tags: [ "os-horizon" ] }
       vars:
-        galera_address: "{{ internal_lb_vip_address }}"
+        horizon_galera_address: "{{ internal_lb_vip_address }}"

tasks/horizon_db_setup.yml

@@ -17,7 +17,7 @@
   mysql_db:
     login_user: "{{ galera_root_user }}"
     login_password: "{{ galera_root_password }}"
-    login_host: "{{ galera_address }}"
+    login_host: "{{ horizon_galera_address }}"
     name: "{{ horizon_galera_database }}"
     state: "present"
   tags:
@@ -27,7 +27,7 @@
   mysql_user:
     login_user: "{{ galera_root_user }}"
     login_password: "{{ galera_root_password }}"
-    login_host: "{{ galera_address }}"
+    login_host: "{{ horizon_galera_address }}"
     name: "{{ horizon_galera_user }}"
     password: "{{ horizon_container_mysql_password }}"
     host: "{{ item }}"

templates/horizon_local_settings.py.j2

@@ -136,7 +136,7 @@ SESSION_ENGINE = "django.contrib.sessions.backends.cached_db"
 DATABASES = {
     'default': {
         'ENGINE': 'django.db.backends.mysql',
-        'HOST': '{{ galera_address }}',
+        'HOST': '{{ horizon_galera_address }}',
         'NAME': '{{ horizon_galera_database }}',
         'USER': '{{ horizon_galera_user }}',
         'PASSWORD': '{{ horizon_container_mysql_password }}',