[Samba] Horrible BIND9_DLZ DNS breakage after DC replaced and samba-tool domain demote --remove-other-dead-server

[Rowland Penny]

OK, this has nothing to do with the classicupgrade, I have setup a
couple of VMs and provisioned a test DC in one and joined another DC in
the other.

I am now at the point the OP is at, samba_dnsupdate cannot add the
required records, all I get in log.samba is this multiple times:

[2016/08/15 15:57:23.949917,  0] ../lib/util/util_runcmd.c:328(samba_runcmd_io_handler)
  /usr/local/samba/sbin/samba_dnsupdate: update failed: NOTAUTH

and it ends with this:

[2016/08/15 15:57:23.975421,  0] ../source4/dsdb/dns/dns_update.c:295(dnsupdate_nameupdate_done)
  ../source4/dsdb/dns/dns_update.c:295: Failed DNS update - NT_STATUS_UNSUCCESSFUL

Now to try and find the cause and fix it.

Rowland