Revert "Remove 'zeroing out empty space' section"
    
    This actually led to the filesystems being bigger.
    The most recent Fedora Rawhide images were ~900MB instead of ~300MB.
    
    Clearly, we need this to make it smaller.
    
    This reverts commit d4d8bffb2cf37a3576f6ad6b6dc68c3c5c5174e1.
    
    Signed-off-by: Neal Gompa <ngompa@fedoraproject.org>