[FAB-2936] Vendor latest version of sarama library

https://jira.hyperledger.org/browse/FAB-2936

This is the first in a series of changesets that will allow us to
quickly query the state of the Kafka cluster. This is itself needed so
that we can decide whether there's a point in repeating a certain
request (e.g. for the creation of a channel/partition in Kafka) or not.

We're vendoring the latest version of the sarama library because it
introduces the `Brokers()` method to the `Client` interface, and this
allows us to easily get the list of active brokers.

This changeset also adds a relevant (and now req'd) config setting, see:
IBM/sarama#816 for more.

Change-Id: Ia6bda8f237e087066f404f09f9d6ac359ed44b85
Signed-off-by: Kostas Christidis <kostas@christidis.io>

orderer/kafka/util.go

@@ -53,16 +53,19 @@ func newBrokerConfig(kafkaVersion sarama.KafkaVersion, chosenStaticPartition int
 		}
 	}
 
+	// Set equivalent of Kafka producer config max.request.bytes to the default
+	// value of a Kafka broker's socket.request.max.bytes property (100 MiB).
+	brokerConfig.Producer.MaxMessageBytes = int(sarama.MaxRequestSize)
+	// 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)
 	// 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)
-	// Set equivalent of Kafka producer config max.request.bytes to the default
-	// value of a Kafka broker's socket.request.max.bytes property (100 MiB).
-	brokerConfig.Producer.MaxMessageBytes = int(sarama.MaxRequestSize)
+	// An esoteric setting required by the sarama library, see:
+	// https://github.com/Shopify/sarama/issues/816
+	brokerConfig.Producer.Return.Successes = true
 
 	brokerConfig.Version = kafkaVersion