subsitute Atomic in the iso volume id
    
    As there is a hard limit for volume id's on isos to be <32 characters,
    we have a list of subsitutions that we maintain to make sure that
    isos all have volume id's under that size. with the addition of
    ppc64le and aarch64 for Atomic host installer the 7 character arch
    length pushed us over the limit using AH for Atomic seems the most
    logical change to make.
    
    Signed-off-by: Dennis Gilmore <dennis@ausil.us>