Fix javadoc:javadoc warnings

- Exclude org.openflow.* from generated javadoc
- Fix warnings

Change-Id: I47aefff15582c6eec05b864fb19613200d07df03
diff --git a/pom.xml b/pom.xml
index eeb61fd..b181b15 100644
--- a/pom.xml
+++ b/pom.xml
@@ -154,7 +154,7 @@
           <charset>UTF-8</charset>
           <locale>en</locale>
           <author>false</author>
-          <excludePackageNames>net.floodlightcontroller.*:net.onrc.onos.core.datastore.serializers</excludePackageNames>
+          <excludePackageNames>net.floodlightcontroller.*:org.openflow.*:net.onrc.onos.core.datastore.serializers</excludePackageNames>
         </configuration>
       </plugin>
 <!-- Remove me when we're sure that system test no longer need JaCoCo