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/model_proxy_manager.go b/ro_core/core/model_proxy_manager.go
index 23261f5..fcf1c78 100644
--- a/ro_core/core/model_proxy_manager.go
+++ b/ro_core/core/model_proxy_manager.go
@@ -18,7 +18,7 @@
 import (
 	"context"
 	"encoding/json"
-	"github.com/opencord/voltha-lib-go/v2/pkg/db/model"
+	"github.com/opencord/voltha-go/db/model"
 	"github.com/opencord/voltha-lib-go/v2/pkg/log"
 	"github.com/opencord/voltha-lib-go/v2/pkg/version"
 	"github.com/opencord/voltha-protos/v2/go/voltha"