SYSDB: Fix sysdb_search_by_name() for looking up groups in MPG domains
If a group was being looked by using sysdb_search_by_name() in a MPG
domain, the code would search only for group objects -- but in a MPG
domain, there may be none, the groups are typically inferred from a user
object.
This could have caused issues e.g. for IPA code with the following
sequence:
getent group aduser@windows.domain
getent passwd aduser@windows.domain
The former would fail to add the fallback subdomain homedir and the latter
would then return a user entry without a homedir, with libc falling back
to the "/" homedir.
Resolves:
https://pagure.io/SSSD/sssd/issue/3615
Reviewed-by: Pavel Březina <pbrezina@redhat.com>