skip disks under scanning when healing disks (#17822)

Bonus:

- avoid calling DiskInfo() calls when missing blocks
  instead heal the object using MRF operation.

- change the max_sleep to 250ms beyond that we will
  not stop healing.

internal/config/heal/heal.go

@@ -97,7 +97,7 @@ var DefaultKVS = config.KVS{
 	},
 	config.KV{
 		Key:   Sleep,
-		Value: "1s",
+		Value: "250ms",
 	},
 	config.KV{
 		Key:   IOCount,