nsswitch: let test_wbinfo.sh also test wbinfo -a $USERNAME@$DOMAIN

nsswitch: let test_wbinfo.sh also test wbinfo -a $USERNAME@$DOMAIN

When winbindd forwards wbinfo -a via netrLogonSamLogon* to a remote
DC work fine for upn names, e.g. administrator@DOMAIN.

But it currently fails locally on a DC against the local sam.

For the RODC only work because it forwards the request to
an RWDC.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13879
BUG: https://bugzilla.samba.org/show_bug.cgi?id=15003

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>