volume: fix memory leak during compaction

fix https://github.com/chrislusf/seaweedfs/issues/1222

weed/server/master_server_handlers_admin.go

@@ -61,7 +61,7 @@ func (ms *MasterServer) volumeVacuumHandler(w http.ResponseWriter, r *http.Reque
 			return
 		}
 	}
-	glog.Infoln("garbageThreshold =", gcThreshold)
+	// glog.Infoln("garbageThreshold =", gcThreshold)
 	ms.Topo.Vacuum(ms.grpcDialOption, gcThreshold, ms.preallocateSize)
 	ms.dirStatusHandler(w, r)
 }