VOL-1497 : Add more control to kv/memory access

- Added kv locking mechanism (etcd only)
- (watch) control path access whenever possible
- (watch) use a transaction for updates and merge with memory
- cleaned up vendoring
- misc changes to fix exceptions found along the way

Amendments:

- Copyright header got removed in auto-generated file
- Changed default locking to false for KV list operation
- Updated backend api to allow the passing of locking parameter

Change-Id: Ie1a55d3ca8b9d92ae71a85ce42bb22fcf1419e2c
diff --git a/vendor/github.com/hashicorp/go-cleanhttp/go.mod b/vendor/github.com/hashicorp/go-cleanhttp/go.mod
new file mode 100644
index 0000000..310f075
--- /dev/null
+++ b/vendor/github.com/hashicorp/go-cleanhttp/go.mod
@@ -0,0 +1 @@
+module github.com/hashicorp/go-cleanhttp