Revert "rebar.config: Don't create extended start script"

This reverts commit 0881c5941a.

The extended start had been enabled intentionally, as some commands
(such as 'ping', 'status', or 'pid') actually do work.

rebar.config

@@ -178,7 +178,7 @@
         {sys_config, "./rel/sys.config"},
         {vm_args, "./rel/vm.args"},
         {overlay_vars, "vars.config"},
-        {extended_start_script, false},
+        {extended_start_script, true},
         {overlay, [{mkdir, "var/log/ejabberd"},
                    {mkdir, "var/lib/ejabberd"},
                    {mkdir, "etc/ejabberd"},