fix keep refreshing partitions issue

In the emitBatch method of PartitionedTridentSpoutExecutor.Emitter, Trident will try to check whether the "_savedCoordinatorMeta" is updated or not by calling ".equals()" method.
But unfortunately, the meta here is the instance of GlobalPartitionInformation, who hasn't override the equals method, so it will directly calling Object.equals().
Thus, even two GlobalPartitionInformation has same broker information, the equals() will return false, and trident will call the _emitter.refreshPartitions method again and again.