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/device_manager.go b/rw_core/core/device_manager.go
index 845542f..2a03dd4 100755
--- a/rw_core/core/device_manager.go
+++ b/rw_core/core/device_manager.go
@@ -18,8 +18,8 @@
 import (
 	"context"
 	"errors"
+	"github.com/opencord/voltha-go/db/model"
 	"github.com/opencord/voltha-go/rw_core/utils"
-	"github.com/opencord/voltha-lib-go/v2/pkg/db/model"
 	"github.com/opencord/voltha-lib-go/v2/pkg/kafka"
 	"github.com/opencord/voltha-lib-go/v2/pkg/log"
 	"github.com/opencord/voltha-lib-go/v2/pkg/probe"