CVE-2020-25717: selftest: Add ad_member_no_nss_wb environment

CVE-2020-25717: selftest: Add ad_member_no_nss_wb environment

This environment creates an AD member that doesn't have
'nss_winbind' configured, while winbindd is still started.

For testing we map a DOMAIN\root user to the local root
account and unix token of the local root user.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14801
BUG: https://bugzilla.samba.org/show_bug.cgi?id=14556

Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>

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