Move most 'universal' tests to Server-dvd-iso
    
    The 'universal' flavor has been kinda pointless for some time
    now. It dates back to the earliest days of openQA, before Pungi
    4 was a thing, when composes were very different; we only built
    a boot.iso and some live images nightly for Rawhide, these
    weren't even formally grouped as a 'compose' at all (fedfind had
    to invent the concept). The TCs/RCs had DVD installer images
    (not *Server* DVD, at the time, just a universal DVD installer).
    We wanted to run some tests on the DVD image if it was available,
    but we still wanted to run them for the nightlies, so we invented
    a whole mechanism for that - this 'universal' flavor, with some
    complicated logic in fedora_openqa which schedules universal on
    the 'best available' image it can find in the compose.
    
    All this is functionally obsolete now. All composes we test are
    now run through Pungi (except the live respins, but they aren't
    relevant here). In current config, the Server DVD is non-failable
    on x86_64 and aarch64, which means it will *always be there* -
    if it fails to build, the compose itself fails, so we won't test
    it. It's failable for ppc64le, but we don't care that much about
    ppc64le; I'm fine with these tests just not running if the Server
    DVD happens to fail in a ppc64le compose.
    
    As a cherry on top, some of the 'universal' tests aren't really
    universal anyway, they fail if you run them on a netinst (off
    the top of my head, all the NFS install tests are like this, as
    we use the ISO to populate the NFS share on the server end).
    
    So let's just move all the tests that actually need an installer
    image to the Server-dvd-iso flavor. Left over in the 'universal'
    flavor are upgrade tests, which don't need an ISO at all - they
    boot from hard disk images and run an upgrade using repos. We
    can change the scheduler logic to be more simple for these, and
    just always schedule them, with no ISO attached. We could even
    rename this flavor 'upgrade', but it might not be worth it.
    
    One slight complication is that the split happened to be helping
    us avoid too many tests in a single support_server cluster; we
    have a cluster of five support_server tests on Server-dvd-iso
    and five support_server tests on universal. I try to avoid the
    clusters getting too big as you need as many worker instances on
    at least one worker host as your largest cluster; if you don't
    have that many, the cluster's tests simply never get scheduled.
    Requiring folks to have at least ten worker instances on one
    host to run these tests is a bit of a big ask. So, to handle
    that, we create a support_server_2 and have the former universal
    tests use that one instead, so we'll have two separate clusters
    on Server-dvd-iso now.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>