In case of disk_image: true user can have raw image, but in packer
template specify qcow2 image format.
Signed-off-by: Vasiliy Tolstov <v.tolstov@selfip.ru>
https://ext4.wiki.kernel.org/index.php/Ext4_VM_Images does not
recommends to dd zero file and deletes it, but in case of enabling
discards and qcow2 image we can recreate qcow2 file with less used
space.
Also qemu-img able to enable compression for qcow2 files, that
sometimes may be useful because it natively supported by qemu.
Signed-off-by: Vasiliy Tolstov <v.tolstov@selfip.ru>