sysdb-tests: sysdb_search_group_by_name with local provider
    
    ldap and local provider are handled differently
    in sysdb_search_group_by_name. And we need to cover both cases to avoid
    regressions.
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3644
    
    Merges: https://pagure.io/SSSD/sssd/pull-request/3720
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>