KAFKA-8748: Fix flaky testDescribeLogDirsRequest (#7182)

The introduction of KIP-480: Sticky Producer Partitioner had the
side effect that generateAndProduceMessages can often write
messages to a lower number of partitions to improve batching.

testDescribeLogDirsRequest (and potentially other tests) relies
on the messages being written somewhat uniformly to the topic
partitions. We fix the issue by including a monotonically
increasing key in the produced messages.

I also included a couple of minor clean-ups I noticed while
debugging the issue.

The test failed very frequently when executed locally before the
change and it passed 100 times consecutively after the change.

Reviewers: Manikumar Reddy <manikumar.reddy@gmail.com>

core/src/test/scala/unit/kafka/server/DescribeLogDirsRequestTest.scala

@@ -57,7 +57,8 @@ class DescribeLogDirsRequestTest extends BaseRequestTest {
     val log1 = servers.head.logManager.getLog(tp1).get
     assertEquals(log0.size, replicaInfo0.size)
     assertEquals(log1.size, replicaInfo1.size)
-    assertTrue(servers.head.logManager.getLog(tp0).get.logEndOffset > 0)
+    val logEndOffset = servers.head.logManager.getLog(tp0).get.logEndOffset
+    assertTrue(s"LogEndOffset '$logEndOffset' should be > 0", logEndOffset > 0)
     assertEquals(servers.head.replicaManager.getLogEndOffsetLag(tp0, log0.logEndOffset, false), replicaInfo0.offsetLag)
     assertEquals(servers.head.replicaManager.getLogEndOffsetLag(tp1, log1.logEndOffset, false), replicaInfo1.offsetLag)
   }

core/src/test/scala/unit/kafka/utils/JaasTestUtils.scala

@@ -155,10 +155,7 @@ object JaasTestUtils {
   val serviceName = "kafka"
 
   def saslConfigs(saslProperties: Option[Properties]): Properties = {
-    val result = saslProperties match {
-      case Some(properties) => properties
-      case None => new Properties
-    }
+    val result = saslProperties.getOrElse(new Properties)
     // IBM Kerberos module doesn't support the serviceName JAAS property, hence it needs to be
     // passed as a Kafka property
     if (Java.isIbmJdk && !result.contains(KafkaConfig.SaslKerberosServiceNameProp))

core/src/test/scala/unit/kafka/utils/TestUtils.scala

@@ -53,7 +53,7 @@ import org.apache.kafka.common.internals.Topic
 import org.apache.kafka.common.network.{ListenerName, Mode}
 import org.apache.kafka.common.record._
 import org.apache.kafka.common.security.auth.SecurityProtocol
-import org.apache.kafka.common.serialization.{ByteArrayDeserializer, ByteArraySerializer, Deserializer, Serializer}
+import org.apache.kafka.common.serialization.{ByteArrayDeserializer, ByteArraySerializer, Deserializer, IntegerSerializer, Serializer}
 import org.apache.kafka.common.utils.Time
 import org.apache.kafka.common.utils.Utils._
 import org.apache.kafka.test.{TestSslUtils, TestUtils => JTestUtils}
@@ -1065,7 +1065,10 @@ object TestUtils extends Logging {
                                  numMessages: Int,
                                  acks: Int = -1): Seq[String] = {
     val values = (0 until numMessages).map(x =>  s"test-$x")
-    val records = values.map(v => new ProducerRecord[Array[Byte], Array[Byte]](topic, v.getBytes))
+    val intSerializer = new IntegerSerializer()
+    val records = values.zipWithIndex.map { case (v, i) =>
+      new ProducerRecord(topic, intSerializer.serialize(topic, i), v.getBytes)
+    }
     produceMessages(servers, records, acks)
     values
   }