tests: sssctl user/group-show basic tests
Add basic tests for sssctl user/group-show commands. This includes
regression test for ticket #3235.
Resolves:
https://fedorahosted.org/sssd/ticket/3235
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>
(cherry picked from commit 35ecfab87a24031e55798b22975e02832ee0f2ad)