rewrite scripts

try to provide better syntax and avoid using bash

debian/templates/image.preinst.in

@@ -1,21 +1,23 @@
-#!/bin/sh -e
+#!/bin/sh
+set -e
 
-version=@abiname@@localversion@
-image_path=/boot/@image-stem@-$version
+if [ "$1" = abort-upgrade ] ; then exit 0 ; fi
 
-if [ "$1" = abort-upgrade ]; then
-    exit 0
-fi
+version='@abiname@@localversion@'
+image_path="/boot/@image-stem@-${version}"
 
 if [ "$1" = install ]; then
     # Create a flag file for postinst
-    mkdir -p /lib/modules/$version
-    touch /lib/modules/$version/.fresh-install
+    mkdir -p "/lib/modules/${version}"
+    touch "/lib/modules/${version}/.fresh-install"
 fi
 
-if [ -d /etc/kernel/preinst.d ]; then
-    DEB_MAINT_PARAMS="$*" run-parts --report --exit-on-error --arg=$version \
-	      --arg=$image_path /etc/kernel/preinst.d
+if [ -d /etc/kernel/preinst.d ] ; then
+    DEB_MAINT_PARAMS="$*" \
+    run-parts --report --exit-on-error \
+      "--arg=${version}" \
+      "--arg=${image_path}" \
+    /etc/kernel/preinst.d
 fi
 
 exit 0