CI: treat ansible-lint warnings as errors

Taken from [1].

[1]: https://ansible.readthedocs.io/projects/lint/configuring/#ansible-lint-configuration

Change-Id: I29c1abb4d518a4da6788e06804f28c5f6853c581

.ansible-lint

 ---
+strict: true
 use_default_rules: true
 skip_list:
   # [E301] Commands should not change things if nothing needs doing