s4-torture/drs: Add test showing that if present in the set the NC root leads and...

s4-torture/drs: Add test showing that if present in the set the NC root leads and tmp_highest_usn moves

The NC root, on any replication when it appears, is the first object to be
replicated, including for all subsequent chunks in the replication.

However the tmp_highest_usn is not updated by that USN, it must
only be updated for the non-NC changes (to match Windows exactly),
or at least only updated with the non-NC changes until it would
naturally appear.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=15401

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