Add Nack handling to CS freshness test and localhop test

Bring implementation of localhop test in line with design

refs #3692

Change-Id: I40c49b68b03aa1996e5546465daaccc18e29853e
diff --git a/test_cs_freshness/test_cs_freshness.py b/test_cs_freshness/test_cs_freshness.py
index f935f7a..4cd6b3e 100644
--- a/test_cs_freshness/test_cs_freshness.py
+++ b/test_cs_freshness/test_cs_freshness.py
@@ -28,7 +28,7 @@
         errormsg = {
             1 : "No data received for first interest",
             2 : "No data received for second interest",
-            3 : "ndn-traffic-server should receive exact 1 interest",
+            3 : "ndn-traffic-server should receive exactly 1 interest",
             4 : "Data received for third interest (expected no data received)",
             5 : "No data received for fourth interest",
         }