ndn: bug fixes in nfdc and experiments

Change-Id: I8cb9b0a9e53e0319e3f18ab6a52867d406a31fd5
diff --git a/ndn/experiments/mcn_failure_experiment.py b/ndn/experiments/mcn_failure_experiment.py
index 019c214..62bdcab 100644
--- a/ndn/experiments/mcn_failure_experiment.py
+++ b/ndn/experiments/mcn_failure_experiment.py
@@ -22,6 +22,7 @@
 # If not, see <http://www.gnu.org/licenses/>.
 
 from ndn.experiments.experiment import Experiment
+from ndn.apps.ndn_ping_client import NDNPingClient
 
 import time
 
@@ -58,7 +59,7 @@
 
         # Restart pings
         for nodeToPing in self.pingedDict[mostConnectedNode]:
-            self.ping(mostConnectedNode, nodeToPing, self.PING_COLLECTION_TIME_AFTER_RECOVERY)
+            NDNPingClient.ping(mostConnectedNode, nodeToPing, self.PING_COLLECTION_TIME_AFTER_RECOVERY)
 
         # Collect pings for more seconds after MCN is up
         time.sleep(self.PING_COLLECTION_TIME_AFTER_RECOVERY)