[FAB-1419] Set appropriate ACK level for brokers

https://jira.hyperledger.org/browse/FAB-1419

By default the partition leader (i.e. the Kafka broker responsible for
maintainig a chain) waits only for the local commit to succeed before
responding.

The right setting to maximize the reliability of data delivery is to have
the partition leader wait for all in-sync replicas (backups) to get a
message before sending back to the producer an acknowledgement or an
error.

Change-Id: I1bc045ef883c39cac3fec2c31f3e9f329ba972c4
Signed-off-by: Kostas Christidis <kostas@christidis.io>

orderer/kafka/util.go

@@ -29,6 +29,10 @@ func newBrokerConfig(kafkaVersion sarama.KafkaVersion, chosenStaticPartition int
 	brokerConfig := sarama.NewConfig()
 
 	brokerConfig.Version = kafkaVersion
+	// Set the level of acknowledgement reliability needed from the broker.
+	// WaitForAll means that the partition leader will wait till all ISRs
+	// got the message before sending back an ACK to the sender.
+	brokerConfig.Producer.RequiredAcks = sarama.WaitForAll
 	// A partitioner is actually not needed the way we do things now,
 	// but we're adding it now to allow for flexibility in the future.
 	brokerConfig.Producer.Partitioner = newStaticPartitioner(chosenStaticPartition)