examples: long_wait py_func/lua_func to exercise Stop

Two extra steps in example_simple.tum that sleep for 10s, used to
verify that pressing Stop interrupts engaged blocking steps.

doc/examples/utils.py

@@ -1,3 +1,5 @@
+from time import sleep
+
 def dummy_exit(useless1, useless2):
     return True
 
@@ -10,4 +12,7 @@ def funcToBeExecuted (bla):
 
 def funcToBeExecuted2 (bla):
     print(bla)
-    return blo
+    return blo
+
+def long_wait (sec):
+    sleep(sec)