USSD: add special 'idle' handler to IUSE for testing

Change-Id: I0d566a60e95ce2da951f22ad47c6155c5b6a338c
diff --git a/tests/test_nodes.vty b/tests/test_nodes.vty
index d9971f7..cf1707a 100644
--- a/tests/test_nodes.vty
+++ b/tests/test_nodes.vty
@@ -51,7 +51,7 @@
   database PATH
   euse NAME
   no euse NAME
-  ussd route prefix PREFIX internal (own-msisdn|own-imsi)
+  ussd route prefix PREFIX internal (own-msisdn|own-imsi|test-idle)
   ussd route prefix PREFIX external EUSE
   no ussd route prefix PREFIX
   ussd default-route external EUSE