apps: Adding ability to ndn::Producer to configure desired fake signature and key locator (key name)

Refs #1008 (http://redmine.named-data.net/)
diff --git a/examples/ndn-simple-with-pcap.cc b/examples/ndn-simple-with-pcap.cc
index 03f3ef4..6499db7 100644
--- a/examples/ndn-simple-with-pcap.cc
+++ b/examples/ndn-simple-with-pcap.cc
@@ -84,10 +84,12 @@
   // Producer will reply to all requests starting with /prefix
   producerHelper.SetPrefix ("/prefix");
   producerHelper.SetAttribute ("PayloadSize", StringValue("1024"));
+  producerHelper.SetAttribute ("Signature", UintegerValue (100));
+  producerHelper.SetAttribute ("KeyLocator", StringValue ("/unique/key/locator"));
   producerHelper.Install (nodes.Get (2)); // last node
 
   PcapWriter trace ("ndn-simple-trace.pcap");
-  Config::ConnectWithoutContext ("/NodeList/*/$ns3::ndn::L3Protocol/FaceList/*/NdnTx",
+  Config::ConnectWithoutContext ("/NodeList/*/DeviceList/*/$ns3::PointToPointNetDevice/MacTx",
 				 MakeCallback (&PcapWriter::TracePacket, &trace));
 
   Simulator::Stop (Seconds (20.0));