auto-t: sleep in wait_for_async_op

This was using a lambda function as input which runs much too fast
for UML to advance the time. Change this to sleep for 100ms between
each check.

This fixes the random hang in testNetconfig.

autotests/util/iwd.py

@@ -111,7 +111,14 @@ def _failure(self, ex):
         self._exception = _convert_dbus_ex(ex)
 
     def _wait_for_async_op(self):
-        ctx.non_block_wait(lambda s: s._is_completed, 30, self, exception=None)
+        def check_complete(s):
+            if s._is_completed:
+                return True
+
+            time.sleep(0.1)
+            return False
+
+        ctx.non_block_wait(check_complete, 30, self, exception=None)
 
         self._is_completed = False
         if self._exception is not None: