This patch fixes two issues:
1) Currently if a broker received StopReplicaRequest with delete=true for the same offline replica, the first StopRelicaRequest will show KafkaStorageException and the second StopRelicaRequest will show ReplicaNotAvailableException. This is because the first StopRelicaRequest will remove the mapping (tp -> ReplicaManager.OfflinePartition) from ReplicaManager.allPartitions before returning KafkaStorageException, thus the second StopRelicaRequest will not find this partition as offline.
This result appears to be inconsistent. And since the replica is already offline and broker will not be able to delete file for this replica, the StopReplicaRequest should fail without making any change and broker should still remember that this replica is offline.
2) Currently if broker receives StopReplicaRequest with delete=true, the broker will attempt to remove future replica for the partition, which will cause KafkaStorageException in the StopReplicaResponse if this replica does not have future replica. It is problematic to always return KafkaStorageException in the response if future replica does not exist.