s3:secrets: add infrastructure to use secrets_domain_infoB to store credentials

s3:secrets: add infrastructure to use secrets_domain_infoB to store credentials

We now store various hashed keys at change time and maintain a lot of details
that will help debugging failed password changes.

We keep storing the legacy values:
 SECRETS/SID/
 SECRETS/DOMGUID/
 SECRETS/MACHINE_LAST_CHANGE_TIME/
 SECRETS/MACHINE_PASSWORD/
 SECRETS/MACHINE_PASSWORD.PREV/
 SECRETS/SALTING_PRINCIPAL/DES/

This allows downgrades to older Samba versions.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=12782

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>