coreos-download: code tidyups
    
    Superficial tidyups, including indentation and comments. Use `h`
    instead of `createElement`, which is less verbose and documented
    by Vue as a common alias [1].
    
    [1] https://vuejs.org/v2/guide/render-function.html#JSX
    
    Signed-off-by: Robert Fairley <rfairley@redhat.com>