Add tests for LoginScreen widget
Add some basic tests for different aspects of LoginScreen such as
'login', 'reset_and_login', 'reset' views.
Fixes: https://pagure.io/freeipa/issue/7619
Reviewed-By: Petr Vobornik <pvoborni@redhat.com>
Reviewed-By: Serhii Tsymbaliuk <stsymbal@redhat.com>