VOL-1097 : Ofagent integration for voltha 2.0

- Created a common location for python based components
- Adjusted the ofagent component to interact with voltha 2.0
- Added streaming rpc methods for rcv/send of packets to voltha api
- Adjusted voltha.proto

Change-Id: I47fb7b80878ead060b4b42bd16cb4f8aa384fdb6
diff --git a/common/core/northbound/grpc/default_api_handler.go b/common/core/northbound/grpc/default_api_handler.go
index 45e8f36..f935462 100644
--- a/common/core/northbound/grpc/default_api_handler.go
+++ b/common/core/northbound/grpc/default_api_handler.go
@@ -261,3 +261,32 @@
 	log.Debugw("SelfTest-request", log.Fields{"id": id})
 	return nil, errors.New("UnImplemented")
 }
+
+func (handler *DefaultAPIHandler) StreamPacketsOut(packetsOut voltha.VolthaService_StreamPacketsOutServer) error {
+	log.Debugw("StreamPacketsOut-request", log.Fields{"packetsOut": packetsOut})
+	return errors.New("UnImplemented")
+}
+
+func (handler *DefaultAPIHandler) ReceivePacketsIn(
+	empty *empty.Empty,
+	packetsIn voltha.VolthaService_ReceivePacketsInServer,
+) error {
+	log.Debugw("ReceivePacketsIn-request", log.Fields{"packetsIn": packetsIn})
+	return errors.New("UnImplemented")
+}
+
+func (handler *DefaultAPIHandler) ReceiveChangeEvents(
+	empty *empty.Empty,
+	changeEvents voltha.VolthaService_ReceiveChangeEventsServer,
+) error {
+	log.Debugw("ReceiveChangeEvents-request", log.Fields{"changeEvents": changeEvents})
+	return errors.New("UnImplemented")
+}
+
+func (handler *DefaultAPIHandler) Subscribe(
+	ctx context.Context,
+	ofAgent *voltha.OfAgentSubscriber,
+) (*voltha.OfAgentSubscriber, error) {
+	log.Debugw("Subscribe-request", log.Fields{"ofAgent": ofAgent})
+	return nil, errors.New("UnImplemented")
+}