add image building script

usr/local/bin/build_image.sh

+#!/bin/bash
+
+img_path="$1"
+
+dnf -y --installroot "$img_path" --releasever=7 install system-release bash yum
+
+rsync -av /var/local/mkosi/mkosi.extra/ "$img_path"
+
+cp /var/local/mkosi/mkosi.postinst "$img_path"
+
+systemd-nspawn -D "$img_path" bash /mkosi.postinst
+