Refactor build scripts

images/02-headers/headers.sh

@@ -0,0 +1,19 @@
+#!/bin/bash
+set -e
+
+DIR=$(readlink /lib/modules/$(uname -r)/build)
+STAMP=${DIR}/.done
+VER=$(basename $DIR)
+URL=https://github.com/rancher/os-kernel/releases/download/${VER}/build.tar.gz
+
+if [ -e $STAMP ]; then
+    echo Headers already installed in $DIR
+    exit 0
+fi
+
+echo Downloading $URL
+mkdir -p $DIR
+wget -O - $URL | gzip -dc | tar xf - -C $DIR
+touch $STAMP
+
+echo Headers installed at $DIR