Comment 4 for bug 1693234

I did some more digging, the ConfigTemplateParser subclass is what ends up stripping these lines away. Allow me to explain. When ConfigTemplateParser is run, it processes the rendered template file 'my.cnf' line-by-line. When it reaches the '!includedir /etc/mysql/conf.d/' statement, it processes the entire string(with the space) as an option name with the value set to None.
Since the value of this option is None, unfortunately it gets stripped away in the _write method here:
https://github.com/openstack/openstack-ansible-plugins/blob/master/action/_v2_config_template.py#L158-L160

It's possible to write in some logic here so it doesn't strip these options away, but I would like @cloudnull's and @odyssey4me's opinion before I move forward.