Imporve healing and reporting (#11312)

* Provide information on *actively* healing, buckets healed/queued, objects healed/failed.
* Add concurrent healing of multiple sets (typically on startup).
* Add bucket level resume, so restarts will only heal non-healed buckets.
* Print summary after healing a disk is done.

cmd/peer-rest-server.go

@@ -947,10 +947,9 @@ func (s *peerRESTServer) BackgroundHealStatusHandler(w http.ResponseWriter, r *h
 		s.writeErrorResponse(w, errors.New("invalid request"))
 		return
 	}
-
 	ctx := newContext(r, w, "BackgroundHealStatus")
 
-	state, ok := getLocalBackgroundHealStatus()
+	state, ok := getBackgroundHealStatus(ctx, newObjectLayerFn())
 	if !ok {
 		s.writeErrorResponse(w, errServerNotInitialized)
 		return