Fixes #7912 - Wizard path error and tests

This PR fixes the problem with the ```container_step_path``` (no step specified and typo) and adds basic tests for the controller.
You should chain a rake task to Foreman's, e.g. https://github.com/theforeman/foreman_plugin_template/blob/master/lib/tasks/foreman_plugin_template_tasks.rake#L22-L31