Handling of table entry messages in P4Runtime

+ synchonized method execution in P4RuntimeClient
+ support for cancellable contexts (for client shutdown)
+ logging of sent/received messages in GrpcControllerImpl
+ minor refactorings

Change-Id: I43f0fcc263579e01957a02ef3392105aed476f33
diff --git a/protocols/grpc/proto/dummy.proto b/protocols/grpc/proto/dummy.proto
index d02b5d8..74268df 100644
--- a/protocols/grpc/proto/dummy.proto
+++ b/protocols/grpc/proto/dummy.proto
@@ -5,7 +5,8 @@
 package dummy;
 
 service DummyService {
-  rpc SayHello (DummyMessageThatNoOneWouldReallyUse) returns (DummyMessageThatNoOneWouldReallyUse) {}
+    rpc SayHello (DummyMessageThatNoOneWouldReallyUse) returns (DummyMessageThatNoOneWouldReallyUse) {
+    }
 }
 
 message DummyMessageThatNoOneWouldReallyUse {