tests: wait a bit for the copy operation

Sending ctrl+shift+c only sends the copy request (XConvertSelection()
call in vmside.c), it doesn't wait for the application to respond. Give
it a moment for the copy to complete.

qubes/tests/integ/basic.py

@@ -513,8 +513,10 @@ async def _test_clipboard(self, test_string,
         # this will be much better - at least because events will have
         # correct timestamp (so gui-daemon would not drop the copy request)
         subprocess.check_call(['xdotool',
-                               'key', 'ctrl+a', 'ctrl+c', 'ctrl+shift+c',
-                               'Escape'])
+                               'key', 'ctrl+a', 'ctrl+c', 'ctrl+shift+c'])
+        # copy operation is async, wait a bit before closing the window
+        await asyncio.sleep(1)
+        subprocess.check_call(['xdotool', 'key', 'Escape'])
 
         await self.wait_for_window_coro(window_title, show=False)