Update image config for renamed Atomic variants
    
    The 'Atomic' variant was renamed 'AtomicHost', and 'Workstation
    Ostree' was renamed 'AtomicWorkstation'. We need to adjust a
    bunch of stuff for this, including the scheduler's list of images
    to schedule jobs for.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>