This adds the --make-tar option which will produce a xz compressed tar
of the root filesystem. This works with either virt-install or no-virt
modes. Use --image-name to set the output filename.
--compression is used to set the compression type to use, which defaults
to xz. Supported types are xz, lzma, gzip and bzip2.
--compress-arg is used to pass arguments to the compression utility.
