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/db/model/child_type_test.go b/db/model/child_type_test.go
new file mode 100644
index 0000000..3836858
--- /dev/null
+++ b/db/model/child_type_test.go
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+
+ * http://www.apache.org/licenses/LICENSE-2.0
+
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package model
+
+import (
+	"github.com/opencord/voltha-protos/v2/go/voltha"
+	"reflect"
+	"testing"
+)
+
+// Dissect a proto message by extracting all the children fields
+func TestChildType_01_Device_Proto_ChildrenFields(t *testing.T) {
+	var cls *voltha.Device
+
+	t.Logf("Extracting children fields from proto type: %s", reflect.TypeOf(cls))
+	names := ChildrenFields(cls)
+	t.Logf("Extracting children field names: %+v", names)
+
+	expectedKeys := []string{"ports", "flows", "flow_groups", "image_downloads", "pm_configs"}
+	for _, key := range expectedKeys {
+		if _, exists := names[key]; !exists {
+			t.Errorf("Missing key:%s from class type:%s", key, reflect.TypeOf(cls))
+		}
+	}
+}
+
+// Verify that the cache contains an entry for types on which ChildrenFields was performed
+func TestChildType_02_Cache_Keys(t *testing.T) {
+	if _, exists := getChildTypes().Cache[reflect.TypeOf(&voltha.Device{}).String()]; !exists {
+		t.Errorf("getChildTypeCache().Cache should have an entry of type: %+v\n", reflect.TypeOf(&voltha.Device{}).String())
+	}
+	for k := range getChildTypes().Cache {
+		t.Logf("getChildTypeCache().Cache Key:%+v\n", k)
+	}
+}