Fix skyline user creation

With previous change [1] when type of role name was changed from string
to a list, variable name change was not reflected in _service_users,
which leads to skipping creation and role assignment to users.

[1] https://review.opendev.org/c/openstack/openstack-ansible-os_skyline/+/918160

Change-Id: Ib5a4af5ea79868b7dd7ee7f4329317815f3b466a

tasks/main.yml

@@ -91,7 +91,7 @@
     _service_users:
       - name: "{{ skyline_service_user_name }}"
         password: "{{ skyline_service_password }}"
-        role: "{{ skyline_role_name }}"
+        role: "{{ skyline_role_names }}"
         domain: "{{ skyline_service_user_domain_id }}"
     _service_endpoints: []
   when: _skyline_is_first_play_host