getncchanges.py: Add a new test for replication

getncchanges.py: Add a new test for replication

This adds a new test to check that if objects are modified during a
replication, then those objects don't wind up missing from the
replication data.

Note that when this scenario occurs, samba returns the objects in a
different order to Windows. This test doesn't care what order the
replicated objects get returned in, so long as they all have been
received by the end of the test.

As part of this, I've refactored _check_replication() in drs_base.py so
it can be reused in new tests. In these cases, the objects are split up
over multiple different chunks. So asserting that the objects are returned
in a specific order makes it difficult to run the same test on both Samba
and Windows.

Signed-off-by: Tim Beale <timbeale@catalyst.net.nz>
Reviewed-by: Garming Sam <garming@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
BUG: https://bugzilla.samba.org/show_bug.cgi?id=12972