Comment 2 for bug 1881133

I prepared a patch I believe solves the issue by using the region IP only if there are no rack IPs for DNS. My test environment, as defined above, consists of 1 Region+rack and 1 remote rack (+ a bunch of custom servers in the separate rack subnet) and after applying the patch, the results look like this:

1. DHCP

ubuntu@maas-rackd:~$ sudo cat /var/lib/maas/dhcpd.conf | grep name-ser
           option domain-name-servers 192.168.200.1, 1.1.1.1, 8.8.8.8, 8.8.4.4;

ubuntu@maas-region:~$ sudo cat /var/lib/maas/dhcpd.conf | grep name-ser
           option domain-name-servers 192.168.122.209;

2. Static/Preseed, deployed on the rack subnet

      nameservers:
        addresses:
        - 192.168.200.1
        - 1.1.1.1
        - 8.8.8.8
        - 8.8.4.4

Now the results are consistent between dynamic and static assignments, and DNS is relayed via the racks, as the documentation says.