New P4RuntimeClient implementation that supports batching and error reporting

The new client API supports batching and provides detailed response for
write requests (e.g. if entity already exists when inserting), which was
not possible with the old one.

This patch includes:
- New more efficient implementation of P4RuntimeClient (no more locking,
use native gRPC executor, use stub deadlines)
- Ported all codecs to new AbstractCodec-based implementation (needed to
implement codec cache in the future)
- Uses batching in P4RuntimeFlowRuleProgrammable and
P4RuntimeGroupActionProgrammable
- Minor changes to PI framework runtime classes

Change-Id: I3fac42057bb4e1389d761006a32600c786598683
diff --git a/core/api/src/main/java/org/onosproject/net/pi/runtime/PiPreReplica.java b/core/api/src/main/java/org/onosproject/net/pi/runtime/PiPreReplica.java
index 4f65e4d..3a03feb 100644
--- a/core/api/src/main/java/org/onosproject/net/pi/runtime/PiPreReplica.java
+++ b/core/api/src/main/java/org/onosproject/net/pi/runtime/PiPreReplica.java
@@ -16,6 +16,7 @@
 
 package org.onosproject.net.pi.runtime;
 
+import com.google.common.annotations.Beta;
 import com.google.common.base.Objects;
 import org.onosproject.net.PortNumber;
 
@@ -29,7 +30,8 @@
  * Each replica is uniquely identified inside a given multicast group or clone
  * session by the pair (egress port, instance ID).
  */
-public class PiPreReplica {
+@Beta
+public final class PiPreReplica {
 
     private final PortNumber egressPort;
     private final int instanceId;