#1065 windows: use shutdown for poweroff and reboot operations

Running ogClient as a service (non interactive user) breaks
poweroff and reboot using ExitWindowsEx function in user32.dll.

Spawn a subshell using os.system and use the 'shutdown' command
instead.

This is a terminating command, we don't need fine grain from
subprocess module.

src/windows/ogOperations.py

@@ -19,10 +19,6 @@ from pystray import Icon, Menu, MenuItem
 from src.ogRest import ThreadState
 
 
-EWX_POWEROFF=0x00000008
-EWX_REBOOT=0x00000002
-
-
 def _create_default_image():
     """
     Creates a default image for the tray icon. Use in case
@@ -75,14 +71,12 @@ class OgWindowsOperations:
         raise NotImplementedError
 
     def poweroff(self):
-        user32 = ctypes.WinDLL('user32')
         systray_p.terminate()
-        user32.ExitWindowsEx(EWX_POWEROFF, 0x0)
+        os.system('shutdown -s -t 0')
 
     def reboot(self):
-        user32 = ctypes.WinDLL('user32')
         systray_p.terminate()
-        user32.ExitWindowsEx(EWX_REBOOT, 0x0)
+        os.system('shutdown -r -t 0')
 
     def shellrun(self, request, ogRest):
         cmd = request.getrun()