createhdds: flip updates_img image over to new updates image
    
    Summary:
    this goes with D799, which changes the updates image tests to
    use a different updates image that works with current anaconda.
    One of the updates image tests is for loading the updates image
    from a hard disk, so we have a hard disk image that contains
    the updates image, so that needs rebuilding with the new update
    image. Simples! This is the first time we use 'imgver', I knew
    it'd come in handy some time...
    
    Test Plan:
    Apply with D799, do `createhdds.py all --clean`, make
    sure the new image is built and the old one removed, run the
    tests and make sure they work (especially install_updates_img_
    local).
    
    Reviewers: jskladan, garretraziel
    
    Reviewed By: garretraziel
    
    Subscribers: tflink
    
    Differential Revision: https://phab.qadevel.cloud.fedoraproject.org/D800