Fix keystone DB Access variable

The DB Access setup for keystone was using the db name and not the user
name. This had no impact because they have the same value.,but if these
were to change at some point it would create an issue.

Change-Id: Ia801ff334ffaa19b37ce4a5ed455a77c705dd3cb

playbooks/os-keystone-install.yml

@@ -136,7 +136,7 @@
         login_user: "{{ galera_root_user }}"
         login_password: "{{ galera_root_password }}"
         login_host: "{{ keystone_galera_address }}"
-        name: "{{ keystone_galera_database }}"
+        name: "{{ keystone_galera_user }}"
         password: "{{ keystone_container_mysql_password }}"
         host: "{{ item }}"
         state: "present"