TEST: Refactor of test_responder_cache_req.c
We need little more in backroung of responder_cache_req tests. There
will be tests which will use three test groups. This patch add support
for it.
Resolves:
https://fedorahosted.org/sssd/ticket/2730
Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>