confdb: sssd tools don't handle the implicit domain
When no sssd.conf exists, sssctl can not read objects from the cache
This happend because implicit files domain is not taken into
account when creating list of domains. With implicit files domain
it should expand at least to this one domain.
Resolves:
https://pagure.io/SSSD/sssd/issue/3769
Reviewed-by: Sumit Bose <sbose@redhat.com>