nsswitch: silence openpam error messages about unexpected responses

nsswitch: silence openpam error messages about unexpected responses

Openpam will log an error message when it receives an unexpected
response. On servers using openpam, convert an unexpected response
into PAM_SERVICE_ERR and log what we're doing so that logging behavior
is more user-configurable.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14416

Signed-off-by: Andrew <awalker@ixsystems.com>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Tue Jun 23 08:08:29 UTC 2020 on sn-devel-184