MessageID has always batch index 0 when sending messages in a batch

[zubchenok]

When I send messages I always get 0 in batchIndex component of MessageID in the result of sendAsync method. Here is a unit test that reproduce the issue:

    @Test
    public void testSameBatchIndex() throws Exception
    {
        String topicName = "persistent://test-prop/vv/ns1/test-" + UUID.randomUUID();
        PulsarClient pulsarClient = PulsarClient.create("pulsar://vv:6650");

        Producer producer = pulsarClient.createProducer(topicName, new ProducerConfiguration()
                .setBatchingEnabled(true)
                .setBatchingMaxMessages(1000)
                .setBatchingMaxPublishDelay(1, TimeUnit.SECONDS)
        );

        Consumer consumer = pulsarClient.subscribe(topicName, "subscription", new ConsumerConfiguration()
                .setMessageListener((consumer1, message) -> System.out.println("Read: " + message.getMessageId()))
        );

        producer.sendAsync("A".getBytes()).whenCompleteAsync((messageId, throwable) -> {
            System.out.println("A: " + messageId);
        });
        producer.sendAsync("B".getBytes()).whenCompleteAsync((messageId, throwable) -> {
            System.out.println("B: " + messageId);
        });
        producer.sendAsync("C".getBytes()).whenCompleteAsync((messageId, throwable) -> {
            System.out.println("C: " + messageId);
        });

        Thread.sleep(3333);

        consumer.close();
        producer.close();
        pulsarClient.close();
    }

Actual output is

A: 1286:0:-1:0
B: 1286:0:-1:0
C: 1286:0:-1:0
Read: 1286:0:-1:0
Read: 1286:0:-1:1
Read: 1286:0:-1:2

Expected output is

A: 1286:0:-1:0
B: 1286:0:-1:1
C: 1286:0:-1:2
Read: 1286:0:-1:0
Read: 1286:0:-1:1
Read: 1286:0:-1:2

version: 1.22.0-incubating