gluon-core: add and use a sysctl Lua module

package/gluon-core/files/lib/gluon/upgrade/core/invariant/013-reboot-on-oom

-#!/bin/sh
+#!/usr/bin/lua
 
-. /lib/gluon/functions/sysctl.sh
+local sysctl = require 'gluon.sysctl'
 
-sysctl_set vm.panic_on_oom 1
+sysctl.set('vm.panic_on_oom', 1)

package/gluon-core/files/usr/lib/lua/gluon/sysctl.lua

+local util = require 'gluon.util'
+
+
+module 'gluon.sysctl'
+
+function set(name, value)
+	util.replace_prefix('/etc/sysctl.conf', name .. '=', name .. '=' .. value .. '\n')
+end