[SPARK-11790][STREAMING][TESTS] Increase the connection timeout

Sometimes, EmbeddedZookeeper may need more than 6 seconds to setup up in a slow Jenkins worker. So just increase the timeout, it won't increase the test time if the test passes.

Author: Shixiong Zhu <shixiong@databricks.com>

Closes #9778 from zsxwing/SPARK-11790.

external/kafka/src/main/scala/org/apache/spark/streaming/kafka/KafkaTestUtils.scala

@@ -52,7 +52,7 @@ private[kafka] class KafkaTestUtils extends Logging {
   // Zookeeper related configurations
   private val zkHost = "localhost"
   private var zkPort: Int = 0
-  private val zkConnectionTimeout = 6000
+  private val zkConnectionTimeout = 60000
   private val zkSessionTimeout = 6000
 
   private var zookeeper: EmbeddedZookeeper = _