Add support for --installpkgs
    
    This allows the user to add specific packages, or package globs, to the
    installer's root via lorax. For example, to build a server product with
    the correct product.img you would pass --installpkgs
    fedora-productimg-server
    
    This removes the need for the kickstart to use --exclude on the repo
    lines and makes it more explicit as to what is being built. This command
    mirrors the same command in lorax.