Add support for P4Runtime clone sessions via Group API

Clone sessions can now be created by defining groups with new type CLONE

The PI framework has been refactored to abstract commonality between
multicast groups and clone sessions as both are managed as part of the
P4Runtime packet replication engine (PRE).

Change-Id: I2f23c629b7de1931d5cab96ec76aef26130ce418
diff --git a/core/api/src/main/java/org/onosproject/net/pi/runtime/PiMulticastGroupEntryHandle.java b/core/api/src/main/java/org/onosproject/net/pi/runtime/PiMulticastGroupEntryHandle.java
index b74ca8e..b18cb51 100644
--- a/core/api/src/main/java/org/onosproject/net/pi/runtime/PiMulticastGroupEntryHandle.java
+++ b/core/api/src/main/java/org/onosproject/net/pi/runtime/PiMulticastGroupEntryHandle.java
@@ -29,7 +29,7 @@
  * ID.
  */
 @Beta
-public final class PiMulticastGroupEntryHandle extends PiHandle {
+public final class PiMulticastGroupEntryHandle extends PiPreEntryHandle {
 
     private final int groupId;
 
@@ -74,8 +74,8 @@
     }
 
     @Override
-    public PiEntityType entityType() {
-        return PiEntityType.PRE_MULTICAST_GROUP_ENTRY;
+    public PiPreEntryType preEntryType() {
+        return PiPreEntryType.MULTICAST_GROUP;
     }
 
     @Override