[SPARK-29580][TESTS] Add kerberos debug messages for Kafka secure tests

### What changes were proposed in this pull request?
`org.apache.spark.sql.kafka010.KafkaDelegationTokenSuite` failed lately. After had a look at the logs it just shows the following fact without any details:
```
Caused by: sbt.ForkMain$ForkError: sun.security.krb5.KrbException: Server not found in Kerberos database (7) - Server not found in Kerberos database
```
Since the issue is intermittent and not able to reproduce it we should add more debug information and wait for reproduction with the extended logs.

### Why are the changes needed?
Failing test doesn't give enough debug information.

### Does this PR introduce any user-facing change?
No.

### How was this patch tested?
I've started the test manually and checked that such additional debug messages show up:
```
>>> KrbApReq: APOptions are 00000000 00000000 00000000 00000000
>>> EType: sun.security.krb5.internal.crypto.Aes128CtsHmacSha1EType
Looking for keys for: kafka/localhostEXAMPLE.COM
Added key: 17version: 0
Added key: 23version: 0
Added key: 16version: 0
Found unsupported keytype (3) for kafka/localhostEXAMPLE.COM
>>> EType: sun.security.krb5.internal.crypto.Aes128CtsHmacSha1EType
Using builtin default etypes for permitted_enctypes
default etypes for permitted_enctypes: 17 16 23.
>>> EType: sun.security.krb5.internal.crypto.Aes128CtsHmacSha1EType
MemoryCache: add 1571936500/174770/16C565221B70AAB2BEFE31A83D13A2F4/client/localhostEXAMPLE.COM to client/localhostEXAMPLE.COM|kafka/localhostEXAMPLE.COM
MemoryCache: Existing AuthList:
#3: 1571936493/200803/8CD70D280B0862C5DA1FF901ECAD39FE/client/localhostEXAMPLE.COM
#2: 1571936499/985009/BAD33290D079DD4E3579A8686EC326B7/client/localhostEXAMPLE.COM
#1: 1571936499/995208/B76B9D78A9BE283AC78340157107FD40/client/localhostEXAMPLE.COM
```

Closes apache#26252 from gaborgsomogyi/SPARK-29580.

Authored-by: Gabor Somogyi <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

external/kafka-0-10-sql/src/test/scala/org/apache/spark/sql/kafka010/KafkaTestUtils.scala

@@ -67,6 +67,8 @@ class KafkaTestUtils(
     secure: Boolean = false) extends Logging {
 
   private val JAVA_AUTH_CONFIG = "java.security.auth.login.config"
+  private val IBM_KRB_DEBUG_CONFIG = "com.ibm.security.krb5.Krb5Debug"
+  private val SUN_KRB_DEBUG_CONFIG = "sun.security.krb5.debug"
 
   private val localCanonicalHostName = InetAddress.getLoopbackAddress().getCanonicalHostName()
   logInfo(s"Local host name is $localCanonicalHostName")
@@ -133,6 +135,7 @@ class KafkaTestUtils(
   private def setUpMiniKdc(): Unit = {
     val kdcDir = Utils.createTempDir()
     val kdcConf = MiniKdc.createConf()
+    kdcConf.setProperty(MiniKdc.DEBUG, "true")
     kdc = new MiniKdc(kdcConf, kdcDir)
     kdc.start()
     kdcReady = true
@@ -238,6 +241,7 @@ class KafkaTestUtils(
     }
 
     if (secure) {
+      setupKrbDebug()
       setUpMiniKdc()
       val jaasConfigFile = createKeytabsAndJaasConfigFile()
       System.setProperty(JAVA_AUTH_CONFIG, jaasConfigFile)
@@ -252,6 +256,14 @@ class KafkaTestUtils(
     }
   }
 
+  private def setupKrbDebug(): Unit = {
+    if (System.getProperty("java.vendor").contains("IBM")) {
+      System.setProperty(IBM_KRB_DEBUG_CONFIG, "all")
+    } else {
+      System.setProperty(SUN_KRB_DEBUG_CONFIG, "true")
+    }
+  }
+
   /** Teardown the whole servers, including Kafka broker and Zookeeper */
   def teardown(): Unit = {
     if (leakDetector != null) {
@@ -303,6 +315,15 @@ class KafkaTestUtils(
       kdc.stop()
     }
     UserGroupInformation.reset()
+    teardownKrbDebug()
+  }
+
+  private def teardownKrbDebug(): Unit = {
+    if (System.getProperty("java.vendor").contains("IBM")) {
+      System.clearProperty(IBM_KRB_DEBUG_CONFIG)
+    } else {
+      System.clearProperty(SUN_KRB_DEBUG_CONFIG)
+    }
   }
 
   /** Create a Kafka topic and wait until it is propagated to the whole cluster */