Generalize api_interface_address variable usage

Useful api_interface_address variable has been define here:
https://github.com/openstack/kolla-ansible/blob/master/ansible/group_vars/all.yml#L57
In order to simplify codebase we must use it as much as possible.

Change-Id: I18fec19bf69e05a22a4142a9cd1165eccd022455

ansible/roles/mariadb/tasks/register.yml

@@ -3,7 +3,7 @@
   kolla_toolbox:
     module_name: mysql_user
     module_args:
-      login_host: "{{ hostvars[inventory_hostname]['ansible_' + api_interface]['ipv4']['address'] }}"
+      login_host: "{{ api_interface_address }}"
       login_port: "{{ mariadb_port }}"
       login_user: "{{ database_user }}"
       login_password: "{{ database_password }}"