winbindd: trigger possible passdb_dsdb initialisation

winbindd: trigger possible passdb_dsdb initialisation

If the passdb backend is passdb_dsdb the domain SID comes from dsdb, not
from secrets.tdb. As we use the domain SID in various places, we must
ensure the domain SID is migrated from dsdb to secrets.tdb before
get_global_sam_sid() is called the first time.

The migration is done as part of the passdb_dsdb initialisation, calling
pdb_get_domain_info() triggers it.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=12729

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Sat Apr  1 21:18:59 CEST 2017 on sn-devel-144

(cherry picked from commit 8b32fc4006ae338ddee7c0e5991958ec3463da0d)