Refactor: move RulePopulatorUtil into util package, w/ minor fixes

Change-Id: I359040c0e81bfcc0acc32a2299782f442f56a1d3
diff --git a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingSnatHandler.java b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingSnatHandler.java
index d4db5a3..b109d2c 100644
--- a/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingSnatHandler.java
+++ b/apps/openstacknetworking/app/src/main/java/org/onosproject/openstacknetworking/impl/OpenstackRoutingSnatHandler.java
@@ -48,6 +48,7 @@
 import org.onosproject.openstacknetworking.api.OpenstackFlowRuleService;
 import org.onosproject.openstacknetworking.api.OpenstackNetworkService;
 import org.onosproject.openstacknetworking.api.OpenstackRouterService;
+import org.onosproject.openstacknetworking.util.RulePopulatorUtil;
 import org.onosproject.openstacknode.api.OpenstackNode;
 import org.onosproject.openstacknode.api.OpenstackNodeService;
 import org.onosproject.store.serializers.KryoNamespaces;