Handle build-args in image names for build cache

#!/usr/bin/env sed -nlf

s/FROM[ ]\{1,\}\([^ ]*:[^ ]*\).*/image \1/p

s/ARG[ ]\{1,\}\([^= ]*\)=\(.*\)/var ${\1:=\2}/p

cache_arg() {

	values

	arg="--cache-from=${RW_CACHE1},${RW_CACHE2},${RW_CACHE3},${RO_CACHE1}"

	sed -n 's/FROM \([^ ]*:[^ ]*\).*/\1/p' Dockerfile |

		while read image; do arg+=",$image"; done

	.gitlab-ci.d/dockerfile-parse.sed Dockerfile |

	while read op value; do

		case $op in

			image) eval "arg+=\",$value\"" ;;

			var) eval ": $value" ;;

		esac

	done

	echo "$arg"

}