gluon-config-mode-core: clean up reboot handling

Don't fork reboot process before all package hooks have been handled and
rendering is complete.

Replace debug.setfenv hack to close stdout with nixio.dup.

Fixes #772

package/gluon-config-mode-core/files/usr/lib/lua/luci/controller/gluon-config-mode/index.lua

@@ -48,7 +48,6 @@ function action_reboot()
   uci:save("gluon-setup-mode")
   uci:commit("gluon-setup-mode")
 
-  if nixio.fork() ~= 0 then
   local fs = require "nixio.fs"
   local util = require "nixio.util"
 
@@ -70,21 +69,21 @@ function action_reboot()
 
   local hostname = uci:get_first("system", "system", "hostname")
 
-    luci.template.render("gluon/config-mode/reboot", { parts=parts
-                                                     , hostname=hostname
-                                                     })
-  else
-    debug.setfenv(io.stdout, debug.getfenv(io.open '/dev/null'))
-    io.stdout:close()
+  luci.template.render("gluon/config-mode/reboot",
+    {
+      parts = parts,
+      hostname = hostname,
+    }
+  )
+
+  if nixio.fork() == 0 then
+    -- Replace stdout with /dev/null
+    nixio.dup(nixio.open('/dev/null', 'w'), nixio.stdout)
 
     -- Sleep a little so the browser can fetch everything required to
     -- display the reboot page, then reboot the device.
-    nixio.nanosleep(2)
-
-    -- Run reboot with popen so it gets its own std filehandles.
-    io.popen("reboot")
+    nixio.nanosleep(1)
 
-    -- Prevent any further execution in this child.
-    os.exit()
+    nixio.execp("reboot")
   end
 end