Use voltha-protos version 4.0.2
Bump major version of voltha-lib-go to 4.0.0 as this change results
in incompatible API version compared to previous version

Change-Id: I1def58361fb1d85f07d6948ebf1ffb7a92eb0d4c
diff --git a/pkg/db/backend_test.go b/pkg/db/backend_test.go
index 98b72a0..78e626b 100644
--- a/pkg/db/backend_test.go
+++ b/pkg/db/backend_test.go
@@ -18,7 +18,7 @@
 
 import (
 	"context"
-	mocks "github.com/opencord/voltha-lib-go/v3/pkg/mocks/etcd"
+	mocks "github.com/opencord/voltha-lib-go/v4/pkg/mocks/etcd"
 	"github.com/phayes/freeport"
 	"github.com/stretchr/testify/assert"
 	"google.golang.org/grpc/codes"