metrics: Use StorageInfo() instead to have consistent info (#9006)

Metrics used to have its own code to calculate offline disks.
StorageInfo() was avoided because it is an expensive operation
by sending calls to all nodes.

To make metrics & server info share the same code, a new
argument `local` is added to StorageInfo() so it will only
query local disks when needed.

Metrics now calls StorageInfo() as server info handler does
but with the local flag set to false.

Co-authored-by: Praveen raj Mani <praveen@minio.io>
Co-authored-by: Harshavardhana <harsha@minio.io>

cmd/healthcheck-handler.go

@@ -60,7 +60,7 @@ func LivenessCheckHandler(w http.ResponseWriter, r *http.Request) {
 	}
 
 	if !globalIsXL && !globalIsDistXL {
-		s := objLayer.StorageInfo(ctx)
+		s := objLayer.StorageInfo(ctx, false)
 		if s.Backend.Type == BackendGateway {
 			if !s.Backend.GatewayOnline {
 				writeResponse(w, http.StatusServiceUnavailable, nil, mimeNone)