fix: admin info output and improve overall performance (#10015)

- admin info node offline check is now quicker
- admin info now doesn't duplicate the code
  across doing the same checks for disks
- rely on StorageInfo to return appropriate errors
  instead of calling locally.
- diskID checks now return proper errors when
  disk not found v/s format.json missing.
- add more disk states for more clarity on the
  underlying disk errors.

cmd/storage-rest-server.go

@@ -134,8 +134,7 @@ func (s *storageRESTServer) DiskInfoHandler(w http.ResponseWriter, r *http.Reque
 	}
 	info, err := s.storage.DiskInfo()
 	if err != nil {
-		s.writeErrorResponse(w, err)
-		return
+		info.Error = err.Error()
 	}
 	defer w.(http.Flusher).Flush()
 	gob.NewEncoder(w).Encode(info)