VOL-1334 : Fixed concurrency issues

- Semaphores were added at the different layers of the model
- Made the proxy interfaces more robust
- Eliminated problems while retrieving latest data in concurrent mode

Change-Id: I7854105d7effa10e5cb704f5d9917569ab184f84
diff --git a/db/model/revision_test.go b/db/model/revision_test.go
index 5a88ff3..a12bf26 100644
--- a/db/model/revision_test.go
+++ b/db/model/revision_test.go
@@ -24,7 +24,7 @@
 	branch := &Branch{}
 	data := &voltha.Device{}
 	children := make(map[string][]Revision)
-	rev := NewNonPersistedRevision(branch, data, children)
+	rev := NewNonPersistedRevision(nil, branch, data, children)
 
 	t.Logf("New revision created: %+v\n", rev)
 }