Test sending NOTIFY(CDS) messages

Test sending NOTIFY(CDS) messages

When starting up the services, send notifies for the existing CDS RRset.
This requires setting up a chain of trust for the test, so the DSYNC
records can be retrieved and validated.

This feature requires enabling 'notify-cds' and 'dnssec-validation'.

In this test, the scanner is pointed to ns2. Since there is no code
for receiving NOTIFY(CDS) messages for delegations, this is treated
as "not authoritative". Checking for this log message ensures us that
the NOTIFY(CDS) message was actually sent.