New openQA tests: update live image build/install

Hot on the heels of adding installer image build/install tests to openQA, I've now added tests which do just the same, but for the Workstation live image. That means that, when running the desktop tests for an update, openQA will also run a test that builds a Workstation live image and a test that boots and installs it. The packages from the update will be used - if relevant - in the live image creation environment, and included in the live image itself. This will allow us to catch problems in updates that relate to the build and basic functionality of live images. Here's an update where you can see that both the installer and live image build tests ran successfully and passed - see the updates-everything-boot-iso and updates-workstation-live-iso flavors. I'm hoping this will help us catch compose issues much more easily during the upcoming Fedora 30 release process.