mvcc: promote db size metrics to "etcd"

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

mvcc/metrics.go

@@ -146,7 +146,7 @@ var (
 		})
 
 	dbTotalSize = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
-		Namespace: "etcd_debugging",
+		Namespace: "etcd",
 		Subsystem: "mvcc",
 		Name:      "db_total_size_in_bytes",
 		Help:      "Total size of the underlying database physically allocated in bytes.",
@@ -159,10 +159,10 @@ var (
 	)
 	// overridden by mvcc initialization
 	reportDbTotalSizeInBytesMu sync.RWMutex
-	reportDbTotalSizeInBytes   func() float64 = func() float64 { return 0 }
+	reportDbTotalSizeInBytes   = func() float64 { return 0 }
 
 	dbTotalSizeInUse = prometheus.NewGaugeFunc(prometheus.GaugeOpts{
-		Namespace: "etcd_debugging",
+		Namespace: "etcd",
 		Subsystem: "mvcc",
 		Name:      "db_total_size_in_use_in_bytes",
 		Help:      "Total size of the underlying database logically in use in bytes.",