Fix for QuotaLimitingStore: Passing storestats for the current store ins...

...tead of the aggregate

The current QuotaLimitingStore limits requests by comparing the current aggregate value against the per store quota value. Changing this so that we compare per store current throughput value with the per store quota value.
But this is coz probably I read this line wrong

```
            StatTrackingStore statStore = new StatTrackingStore(store, this.storeStats);
```

& ended up passing the 'parent' storeStats object..