Restore original user after sorcery logout

Sorcery calls reset_session on [logout](https://github.com/NoamB/sorcery/blob/master/lib/sorcery/controller.rb#L55) which wipes the whole session including `original_user_scope_identifier`, which breaks the switch-back feature.

This change is more specific for sorcery. If other providers do the same this should be moved to `login_exclusive` method to affect all providers.