selftest: Make sure single-link conflict retains the deleted link

selftest: Make sure single-link conflict retains the deleted link

There should only ever be one active value for a single-valued link
attribute. When a conflict occurs the 'losing' value should still be
present, but should be marked as deleted.

This change is just making the test criteria stricter to make sure that
we fix the bug correctly.

Note that the only way to query the deleted link attributes present
is to send a DRS request.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=13055

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Garming Sam <garming@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>