VOL-2154 : Moving back db/model to voltha-go repo

- Package imports and dockerfiles updated
- Left backend.go in voltha-lib-go

Amendments:

- Adjusted proto imports in unit tests
- Adjusted references to db/model in unit tests
- Integrate voltha-lib-go updates

Change-Id: I2d168c516a238222f0371a7bcb672d2b06796838
diff --git a/rw_core/core/core.go b/rw_core/core/core.go
index ee0bd76..e340a29 100644
--- a/rw_core/core/core.go
+++ b/rw_core/core/core.go
@@ -17,9 +17,10 @@
 
 import (
 	"context"
+	"github.com/opencord/voltha-go/db/model"
 	"github.com/opencord/voltha-go/rw_core/config"
+	"github.com/opencord/voltha-lib-go/v2/pkg/db"
 	"github.com/opencord/voltha-lib-go/v2/pkg/db/kvstore"
-	"github.com/opencord/voltha-lib-go/v2/pkg/db/model"
 	grpcserver "github.com/opencord/voltha-lib-go/v2/pkg/grpc"
 	"github.com/opencord/voltha-lib-go/v2/pkg/kafka"
 	"github.com/opencord/voltha-lib-go/v2/pkg/log"
@@ -63,7 +64,7 @@
 	core.kafkaClient = kafkaClient
 
 	// Setup the KV store
-	backend := model.Backend{
+	backend := db.Backend{
 		Client:     kvClient,
 		StoreType:  cf.KVStoreType,
 		Host:       cf.KVStoreHost,