Use OpenStack-Infra MariaDB mirror in OpenStack-CI

When executing tests within OpenStack-CI, the MariaDB
mirror implemented in CopenStack-Infra will be used
instead of the Rackspace mirror.

This should speed up OpenStack-CI testing and be more
reliable as it eliminates external dependencies and
does not rely on a single mirror as a source.

For the sake of record, the MariaDB mirror was
implemented in OpenStack-Infra with these reviews:

- https://review.openstack.org/307831
- https://review.openstack.org/354203
- https://review.openstack.org/440769

Change-Id: I7254bc246525488f1b94a3835786307057a906c1

tests/roles/bootstrap-host/tasks/prepare_aio_config.yml

@@ -72,6 +72,13 @@
     - nodepool_dir.stat.exists
     - bootstrap_host_ubuntu_repo is defined
 
+- name: Set the MariaDB repository URL in OpenStack-CI
+  set_fact:
+    galera_repo_url: "{{ bootstrap_host_ubuntu_repo | netorigin }}/ubuntu-mariadb/10.1"
+  when:
+    - nodepool_dir.stat.exists
+    - bootstrap_host_ubuntu_repo is defined
+
 - name: Set the package cache timeout to 60 mins in OpenStack-CI
   set_fact:
     cache_timeout: 3600

tests/roles/bootstrap-host/templates/user_variables.aio.yml.j2

@@ -68,6 +68,12 @@ repo_build_pip_extra_indexes:
 uca_apt_repo_url: {{ uca_apt_repo_url }}
 {% endif %}
 
+{% if galera_repo_url is defined %}
+## MariaDB mirror to use
+galera_repo_url: {{ galera_repo_url }}
+galera_client_apt_repo_url: {{ galera_repo_url }}
+{% endif %}
+
 {% if cache_timeout is defined %}
 ## Package cache timeout
 cache_timeout: {{ cache_timeout }}