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/branch_test.go b/db/model/branch_test.go
new file mode 100644
index 0000000..cf8406c
--- /dev/null
+++ b/db/model/branch_test.go
@@ -0,0 +1,109 @@
+/*
+ * 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 (
+	"crypto/md5"
+	"fmt"
+	"testing"
+)
+
+var (
+	TestBranch_BRANCH *Branch
+	TestBranch_HASH   string
+)
+
+// Create a new branch and ensure that fields are populated
+func TestBranch_NewBranch(t *testing.T) {
+	node := &node{}
+	hash := fmt.Sprintf("%x", md5.Sum([]byte("origin_hash")))
+	origin := &NonPersistedRevision{
+		Config:   &DataRevision{},
+		Children: make(map[string][]Revision),
+		Hash:     hash,
+		Branch:   &Branch{},
+	}
+	txid := fmt.Sprintf("%x", md5.Sum([]byte("branch_transaction_id")))
+
+	TestBranch_BRANCH = NewBranch(node, txid, origin, true)
+	t.Logf("New Branch(txid:%s) created: %+v\n", txid, TestBranch_BRANCH)
+
+	if TestBranch_BRANCH.Latest == nil {
+		t.Errorf("Branch latest pointer is nil")
+	} else if TestBranch_BRANCH.Origin == nil {
+		t.Errorf("Branch origin pointer is nil")
+	} else if TestBranch_BRANCH.Node == nil {
+		t.Errorf("Branch node pointer is nil")
+	} else if TestBranch_BRANCH.Revisions == nil {
+		t.Errorf("Branch revisions map is nil")
+	} else if TestBranch_BRANCH.Txid == "" {
+		t.Errorf("Branch transaction id is empty")
+	}
+}
+
+// Add a new revision to the branch
+func TestBranch_AddRevision(t *testing.T) {
+	TestBranch_HASH = fmt.Sprintf("%x", md5.Sum([]byte("revision_hash")))
+	rev := &NonPersistedRevision{
+		Config:   &DataRevision{},
+		Children: make(map[string][]Revision),
+		Hash:     TestBranch_HASH,
+		Branch:   &Branch{},
+	}
+
+	TestBranch_BRANCH.AddRevision(rev)
+	t.Logf("Added revision: %+v\n", rev)
+
+	if len(TestBranch_BRANCH.Revisions) == 0 {
+		t.Errorf("Branch revisions map is empty")
+	}
+}
+
+// Ensure that the added revision can be retrieved
+func TestBranch_GetRevision(t *testing.T) {
+	if rev := TestBranch_BRANCH.GetRevision(TestBranch_HASH); rev == nil {
+		t.Errorf("Unable to retrieve revision for hash:%s", TestBranch_HASH)
+	} else {
+		t.Logf("Got revision for hash:%s rev:%+v\n", TestBranch_HASH, rev)
+	}
+}
+
+// Set the added revision as the latest
+func TestBranch_LatestRevision(t *testing.T) {
+	addedRevision := TestBranch_BRANCH.GetRevision(TestBranch_HASH)
+	TestBranch_BRANCH.SetLatest(addedRevision)
+
+	rev := TestBranch_BRANCH.GetLatest()
+	t.Logf("Retrieved latest revision :%+v", rev)
+
+	if rev == nil {
+		t.Error("Unable to retrieve latest revision")
+	} else if rev.GetHash() != TestBranch_HASH {
+		t.Errorf("Latest revision does not match hash: %s", TestBranch_HASH)
+	}
+}
+
+// Ensure that the origin revision remains and differs from subsequent revisions
+func TestBranch_OriginRevision(t *testing.T) {
+	rev := TestBranch_BRANCH.Origin
+	t.Logf("Retrieved origin revision :%+v", rev)
+
+	if rev == nil {
+		t.Error("Unable to retrieve origin revision")
+	} else if rev.GetHash() == TestBranch_HASH {
+		t.Errorf("Origin revision should differ from added revision: %s", TestBranch_HASH)
+	}
+}