test stork with latest bind9 (9.17.x)

There's a report #467 (closed) that complains about Stork 0.14 not working with bind 9.17.8. As of today, we're using an old bind 9.11.x in the stork demo. And that's probably about it how closely we test it.

The goal of this ticket to figure out how to test Stork with recent BIND9 versions. One way (but certainly not the only one) is to update one of the containers we have in demo (there are two: agent-bind9 and agent-bind9-2) to use the latest bind version.

Whatever the testing practice is, it should be reasonably easy to update the bind version. The overall goal is to keep up with the reasonably latest BIND releases.

Another potential explanation for the issues in #467 (closed) is that the demo used native packages provided by Ubuntu. The submitter of #467 (closed) seems to have used BIND9 packages provided by ISC.