[ONOS-6163] (vnet) revise intent service for vnets

Revise intent service for virtual networks.

Change-Id: I4955cde2296e58d8f0e356d19483e84f51193318
diff --git a/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/intent/phase/VirtualFinalIntentProcessPhase.java b/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/intent/phase/VirtualFinalIntentProcessPhase.java
new file mode 100644
index 0000000..978c95c
--- /dev/null
+++ b/incubator/net/src/main/java/org/onosproject/incubator/net/virtual/impl/intent/phase/VirtualFinalIntentProcessPhase.java
@@ -0,0 +1,46 @@
+/*
+ * Copyright 2017-present Open Networking Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.incubator.net.virtual.impl.intent.phase;
+
+import org.onosproject.net.intent.IntentData;
+
+import java.util.Optional;
+
+/**
+ * Represents a final phase of processing an intent for virtual networks.
+ */
+public abstract class VirtualFinalIntentProcessPhase
+        implements VirtualIntentProcessPhase {
+
+    @Override
+    public final Optional<VirtualIntentProcessPhase> execute() {
+        preExecute();
+        return Optional.empty();
+    }
+
+    /**
+     * Executes operations that must take place before the phase starts.
+     */
+    protected void preExecute() {}
+
+    /**
+     * Returns the IntentData object being acted on by this phase.
+     *
+     * @return intent data object for the phase
+     */
+    public abstract IntentData data();
+}