Add unit tests fir DefaultFlowEntry class

Also fixed a bug where the error DefaultFlowEntry was not setting the
timestamp.

Change-Id: Ic23e91926605ea7c166b244d8352b58347844a5f
diff --git a/core/api/src/main/java/org/onlab/onos/net/flow/DefaultFlowEntry.java b/core/api/src/main/java/org/onlab/onos/net/flow/DefaultFlowEntry.java
index c2d901b..c6cb361 100644
--- a/core/api/src/main/java/org/onlab/onos/net/flow/DefaultFlowEntry.java
+++ b/core/api/src/main/java/org/onlab/onos/net/flow/DefaultFlowEntry.java
@@ -80,6 +80,7 @@
         this.state = FlowEntryState.FAILED;
         this.errType = errType;
         this.errCode = errCode;
+        this.lastSeen = System.currentTimeMillis();
     }
 
     @Override