In order to disable predictable network interface naming, "net.ifnames=0" is appended to GRUB_CMDLINE_LINUX in /etc/default/grub.
In image_creator/os_type/linux.py the author mentioned "The variable could have a value foo or 'foo' or "foo". Appending ' bar' will lead to a valid result."
The image made will have this line GRUB_CMDLINE_LINUX=""' net.ifname=0' in Ubuntu 18.04 and does not work any more.