instrumentation: instrumentation for locks. (#2584)

- Instrumentation for locks.
- Detailed test coverage.
- Adding RPC control handler to fetch lock instrumentation.
- RPC control handlers suite tests with a test RPC server.

cmd/control-main.go

@@ -24,6 +24,7 @@ var controlCmd = cli.Command{
 	Usage:  "Control and manage minio server.",
 	Action: mainControl,
 	Subcommands: []cli.Command{
+		lockCmd,
 		healCmd,
 		shutdownCmd,
 	},