getncchanges.py: Add test for adding links during replication

getncchanges.py: Add test for adding links during replication

We have identified a case where the Samba server can send linked
attributes but not the target object. In this case, the Samba DRS client
would hit the "Failed to re-resolve GUID" case in replmd and silently
discard the linked attribute.

However, Samba will resend the linked attribute in the next cycle
(because its USN is still higher than the committed HWM), so it should
recover OK. On older releases, this may have caused problems if the
first error resulting in a hanging link (which might mean the second
time it's processed it still fails to be added).

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