CVE-2020-25717: selftest: turn ad_member_no_nss_wb into ad_member_idmap_nss

CVE-2020-25717: selftest: turn ad_member_no_nss_wb into ad_member_idmap_nss

In reality environments without 'nss_winbind' make use of 'idmap_nss'.

For testing, DOMAIN/bob is mapped to the local 'bob',
while DOMAIN/jane gets the uid based on the local 'jane'
vis idmap_nss.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14901

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

Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
[metze@samba.org avoid to create a new ad_member_idmap_nss environment
and merge it with ad_member_no_nss_wb instead]
Reviewed-by: Ralph Boehme <slow@samba.org>
(cherry picked from commit 8a9f2aa2c1cdfa72ad50d7c4f879220fe37654cd)