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/ro_core/core/device_agent_test.go b/ro_core/core/device_agent_test.go
index f8d8d45..bb87fac 100644
--- a/ro_core/core/device_agent_test.go
+++ b/ro_core/core/device_agent_test.go
@@ -16,8 +16,9 @@
 package core
 
 import (
+	"github.com/opencord/voltha-go/db/model"
 	"github.com/opencord/voltha-go/ro_core/config"
-	"github.com/opencord/voltha-lib-go/v2/pkg/db/model"
+	"github.com/opencord/voltha-lib-go/v2/pkg/db"
 	"github.com/opencord/voltha-protos/v2/go/voltha"
 	"github.com/stretchr/testify/assert"
 	"testing"
@@ -28,7 +29,7 @@
 	var core Core
 	core.instanceId = "ro_core"
 	core.config = config.NewROCoreFlags()
-	backend := model.Backend{
+	backend := db.Backend{
 		Client:     core.kvClient,
 		StoreType:  core.config.KVStoreType,
 		Host:       core.config.KVStoreHost,