Revert two disk sizes that got accidentally bumped as versions
    
    These disk sizes are meant to be 40. It looks like someone did
    s/40/41/ and then s/41/42/ when doing version bumps to 41 and
    42, and didn't catch that the changes to disk_size here were
    bogus.
    
    Signed-off-by: Adam Williamson <awilliam@redhat.com>