Download by ADVISORY_NVRS with koji for updates, not ADVISORY
    
    This goes with a corresponding fedora_openqa commit that passes
    ADVISORY_NVRS when scheduling update jobs. This is to address
    https://pagure.io/fedora-qa/fedora_openqa/issue/78 so we can
    publish spec-compliant and correct CI Messages: we will decide
    what NVRs are in the update at scheduling time and always get
    and test those NVRs, rather than the test downloading whatever
    is in the update when it is run.
    
    Some consequences: manual restarting or cloning of an update
    test scheduled before this change lands will result in failure;
    to do this you'll have to add the ADVISORY_NVRS value manually
    with clone_job.pl, or simply reschedule the update with
    fedora-openqa.
    
    Manual restarting or cloning of an update test scheduled with
    this change will always test the same NVRs. If the update has
    changed and you want to re-test with the new packages in the
    update, you must change ADVISORY_NVRS manually with clone_job,
    or reschedule with fedora-openqa.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>