sim_vehicle.py: avoid requesting process name on zombie process

This method does on OSX - in a non-catchable way prior to Py3

Tools/autotest/sim_vehicle.py

@@ -113,6 +113,8 @@ def kill_tasks():
 
     import psutil
     for proc in psutil.process_iter():
+        if proc.status() == psutil.STATUS_ZOMBIE:
+            continue
         if proc.name() in victim_names:
             proc.kill()