Move sparsify to be after all packages are installed

This creates a much smaller resulting base image (< 1GB each)
Fix virt-sysprep options that have changed in new releases

Use --operations to remove ssh-userdir instead of grepping for all defaults
and constructing a string of operations to disable
Remove --no-selinux-relabel as that operation looks like it has been removed
Split rdo-demo-prep so that the packstack install is done via a new script