The problem:

- Some tests are removing all plugins (plugin_test, rabl_test, belongs_to_proxy_test) from the registry. This has, among others, one important consequence: the plugin permissions are removed.
 - Take an example. Foreman Ansible overrides the Host#form with a list of 'Ansible Roles' to choose.
 - When the view for this Host#form is rendered (e.g: a HostController or HostJSTest), the list of 'Ansible Roles' has also to be rendered.
 - Since a previous test removed the plugin from the `Foreman::Plugin.all` registry, but the plugin is still installed as a Rails Engine, the overrides by deface still apply.
 - Some tests that render the Host form fail to run as rendering is impossible without the 'ansible_roles' permission. These permissions are only loaded in tests if the plugin is registered in Foreman::Plugin*

Foreman::Plugin::RbacRegistry should not be cleared https://github.com/theforeman/foreman/blob/develop/test/fixtures/permissions.yml#L772

To fix this, I suggest adding a helper method to our test_helper to handle removing & restoring.