Enable checkstyle rule that looks for final classes.

Enabled the checkstyle rule that checks if classes that could
be final are made final, and fixed the violations that were
reported.

Change-Id: I07ca27f420855116959c1bef3648330cd266ddd8
diff --git a/src/main/java/net/onrc/onos/core/datastore/DataStoreClient.java b/src/main/java/net/onrc/onos/core/datastore/DataStoreClient.java
index be9fce5..b5c1ae7 100644
--- a/src/main/java/net/onrc/onos/core/datastore/DataStoreClient.java
+++ b/src/main/java/net/onrc/onos/core/datastore/DataStoreClient.java
@@ -4,7 +4,7 @@
 import net.onrc.onos.core.datastore.ramcloud.RCClient;
 
 // This class probably need to be a service
-public class DataStoreClient {
+public final class DataStoreClient {
     private static final String BACKEND = System.getProperty("net.onrc.onos.core.datastore.backend", "hazelcast");
 
     // Suppresses default constructor, ensuring non-instantiability.