Update the volume ID substitutions list
    
    Some newer subvariants / loadouts were missing from the
    substitution list. This updates it, alphabetizes it, corrects
    the indentation, and adds a better comment about what it's for.
    
    Note https://pagure.io/koji/pull-request/817 , corresponding
    pull request for Koji.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>