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/PiEntityType.java b/core/api/src/main/java/org/onosproject/net/pi/runtime/PiEntityType.java
index 0e99188..2dc7235 100644
--- a/core/api/src/main/java/org/onosproject/net/pi/runtime/PiEntityType.java
+++ b/core/api/src/main/java/org/onosproject/net/pi/runtime/PiEntityType.java
@@ -54,14 +54,9 @@
     COUNTER_CELL("counter cell"),
 
     /**
-     * Packet Replication Engine (PRE) multicast group entry.
+     * Packet Replication Engine (PRE) entry.
      */
-    PRE_MULTICAST_GROUP_ENTRY("PRE multicast group entry"),
-
-    /**
-     * Packet Replication Engine (PRE) clone session entry.
-     */
-    PRE_CLONE_SESSION_ENTRY("PRE clone session entry");
+    PRE_ENTRY("PRE entry");
 
     private final String humanReadableName;