Fix extlinux mbr installation
Reduce the appliance disk size if possible
Simplified restore function of qcow2 checkpoint
Installed linux kernel and extlinux bootloader from bootstrap step
Used disk manipulation steps on bootstrap OR export section
Get separated bootloader installation step
Avoid error messages from nullify freespace step
delete redundant microsteps from build_appliance_from_docker
Removed nullify freespace microsteps because it's too slow
Fixed broken recipes