convert docker images to rootfs

Motiejus Jakštys ce8ce9f59e stdout is -		2021-05-24 00:11:58 +03:00
rootfs	'want' can also accept different types	2021-05-24 00:11:58 +03:00
BUILD	error reporting	2021-05-24 00:11:58 +03:00
main.go	stdout is -	2021-05-24 00:11:58 +03:00