Fix Kafka container-test when running on CI

Do not assume that the Kafka container-based tests are run
with a local Docker server: get the actual bootstrap server
details from the container itself.

On the Gerrit-CI the Docker servers can be remote and
therefore the bootstrap server won't be available on localhost.

Change-Id: I607d320666627dd89352f81592e056e670b227d8

src/test/java/com/googlesource/gerrit/plugins/kafka/api/KafkaBrokerApiTest.java

diff --git a/src/test/java/com/googlesource/gerrit/plugins/kafka/api/KafkaBrokerApiTest.java b/src/test/java/com/googlesource/gerrit/plugins/kafka/api/KafkaBrokerApiTest.java
index 9078d05..eafa191 100644
--- a/src/test/java/com/googlesource/gerrit/plugins/kafka/api/KafkaBrokerApiTest.java
+++ b/src/test/java/com/googlesource/gerrit/plugins/kafka/api/KafkaBrokerApiTest.java
@@ -141,7 +141,7 @@
   public static void beforeClass() throws Exception {
     kafka = new TestKafkaContainer();
     kafka.start();
-    System.setProperty(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, "localhost:9093");
+    System.setProperty(ProducerConfig.BOOTSTRAP_SERVERS_CONFIG, kafka.getBootstrapServers());
 
     Injector baseInjector = Guice.createInjector(new TestModule());
     WorkQueue testWorkQueue = baseInjector.getInstance(WorkQueue.class);