tests: Add getncchanges test for cross-partition links + TGT

tests: Add getncchanges test for cross-partition links + TGT

This adds a test-case to highlight a bug in the client side GetNCChanges
handling.

These tests mostly exercise the server-side behaviour of sending the
GetNCChanges, however, there's a bug in the client-side code when we try
to handle a missing cross-partition link target *in combination* with
the GET_TGT flag already having been set.

The test is exercising the client-side code by using the 'samba-tool drs
replicate' command. By adding a one-way link to a deleted target object,
we force the client code to retry with the GET_TGT flag set.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14022

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