[ONOS-5473] Defining VirtualFlowRuleProvider interface.

Changes
1. Defined provider/registry structure for virtual providers
2. Added VirtualFlowRuleProvider
3. Added VirtualFlowRuleProivderService
4. Added VirtaulFlowRuleProviderRegistry

Change-Id: I3aa0eaee050177d06cade88c63df13f165ca5cf2
diff --git a/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/provider/package-info.java b/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/provider/package-info.java
new file mode 100644
index 0000000..36cd14d
--- /dev/null
+++ b/incubator/api/src/main/java/org/onosproject/incubator/net/virtual/provider/package-info.java
@@ -0,0 +1,20 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * 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.
+ */
+
+/**
+ * Network virtualization data models and services.
+ */
+package org.onosproject.incubator.net.virtual.provider;
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