Using different defaults about logging for vs/pure-ftpd (bnc#888287)

also added test
Just nit picking: I'd rather prefer putting large mock data into separate files (fixtures). In this case it's not that big like in [available_addons.yml](https://github.com/yast/yast-registration/blob/master/test/fixtures/available_addons.yml), but still makes sense IMHO.

(Ideally define a helper method in [spec_helper.rb](https://github.com/yast/yast-registration/blob/master/test/spec_helper.rb#L31) and then [use it in tests](https://github.com/yast/yast-registration/blob/master/test/ssl_certificate_spec.rb#L13).)

Then you can easily share the data in more tests.