[FLINK-7739] [kafka connector] Fix test instabilities

  - Set shorter heartbeats intervals. Default pause value of 60seconds is
    too large (tests would timeout before akka react)

  - Exclude netty dependency from zookeeper. Zookeeper was pulling in
    conflicting Netty version. Conflict was extremly subtle - TaskManager in
    Kafka tests was deadlocking in some rare corner cases.

This closes #4775

flink-connectors/flink-connector-kafka-base/src/test/java/org/apache/flink/streaming/connectors/kafka/KafkaTestBase.java

@@ -18,6 +18,7 @@
 package org.apache.flink.streaming.connectors.kafka;
 
 import org.apache.flink.client.program.ProgramInvocationException;
+import org.apache.flink.configuration.AkkaOptions;
 import org.apache.flink.configuration.ConfigConstants;
 import org.apache.flink.configuration.Configuration;
 import org.apache.flink.configuration.MetricOptions;
@@ -121,6 +122,8 @@ public abstract class KafkaTestBase extends TestLogger {
 
 	protected static Configuration getFlinkConfiguration() {
 		Configuration flinkConfig = new Configuration();
+		flinkConfig.setString(AkkaOptions.WATCH_HEARTBEAT_PAUSE, "5 s");
+		flinkConfig.setString(AkkaOptions.WATCH_HEARTBEAT_INTERVAL, "1 s");
 		flinkConfig.setInteger(ConfigConstants.LOCAL_NUMBER_TASK_MANAGER, NUM_TMS);
 		flinkConfig.setInteger(ConfigConstants.TASK_MANAGER_NUM_TASK_SLOTS, TM_SLOTS);
 		flinkConfig.setLong(TaskManagerOptions.MANAGED_MEMORY_SIZE, 16L);

pom.xml

@@ -460,6 +460,12 @@ under the License.
 						<groupId>org.slf4j</groupId>
 						<artifactId>slf4j-log4j12</artifactId>
 					</exclusion>
+					<!-- Netty from zookeeper is conflicting with akka's, which can cause occasional deadlock inside
+					Netty threads -->
+					<exclusion>
+						<groupId>io.netty</groupId>
+						<artifactId>netty</artifactId>
+					</exclusion>
 				</exclusions>
 			</dependency>