VOL-1775 VOL-1779 VOL-1780 : Fix several issues with overall stability

- Apply changes as reported by golang race utility
- Added version attribute in KV object
- Added context object to db/model api
- Carrying timestamp info through context to help in the
  decision making when applying a revision change
- Replaced proxy access control mechanism with etcd reservation mechanism

Change-Id: If3d142a73b1da0d64fa6a819530f297dbfada2d3
diff --git a/ro_core/core/model_proxy.go b/ro_core/core/model_proxy.go
index f5e6c3b..473e579 100644
--- a/ro_core/core/model_proxy.go
+++ b/ro_core/core/model_proxy.go
@@ -16,6 +16,7 @@
 package core
 
 import (
+	"context"
 	"github.com/opencord/voltha-go/common/log"
 	"github.com/opencord/voltha-go/db/model"
 	"google.golang.org/grpc/codes"
@@ -55,7 +56,7 @@
 
 	log.Debugw("get-data", log.Fields{"path": path})
 
-	if data := mp.rootProxy.Get(path, 1, false, ""); data != nil {
+	if data := mp.rootProxy.Get(context.Background(), path, 1, false, ""); data != nil {
 		return data, nil
 	}
 	return nil, status.Errorf(codes.NotFound, "data-path: %s", path)