CLOUDSTACK-7143: cleanup configure_gruh.sh code

Adding a check whether GRUB_TIMEOUT has already been set, and if it has,
skip re-running update-grub.

tools/appliance/definitions/systemvmtemplate/configure_grub.sh

@@ -1,5 +1,13 @@
+#!/bin/bash
+
+set -e
+set -x
+
 # Remove 5s grub timeout to speed up booting
-cat <<EOF > /etc/default/grub
+function configure_grub() {
+  grep GRUB_TIMEOUT=0 /etc/default/grub && return
+
+  cat <<EOF > /etc/default/grub
 # If you change this file, run 'update-grub' afterwards to update
 # /boot/grub/grub.cfg.
 
@@ -10,4 +18,7 @@ GRUB_CMDLINE_LINUX_DEFAULT="quiet"
 GRUB_CMDLINE_LINUX="debian-installer=en_US"
 EOF
 
-update-grub
+  update-grub
+}
+
+return 2>/dev/null || configure_grub