Add a uuid for producer name so several producers can run at the same time (#24)

The goal here is to allow the output plugin to run several producers. 
While testing with the current build I experienced some issues that it wouldn't handle multiple producers with the same name so this is my solution to solve that issue.

Author: Andyandpandy

src/main/java/org/apache/pulsar/logstash/outputs/Pulsar.java

@@ -27,6 +27,7 @@
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
+import java.util.UUID;
 import java.util.concurrent.CountDownLatch;
 
 @LogstashPlugin(name = "pulsar")
@@ -243,7 +244,8 @@ private org.apache.pulsar.client.api.Producer<byte[]> getProducer(String topic)
                     .blockIfQueueFull(blockIfQueueFull)
                     .compressionType(getSubscriptionType());
             if (producerName != null) {
-                producerBuilder.producerName(producerName);
+                String uniqProducerName = producerName + '-' + UUID.randomUUID();
+                producerBuilder.producerName(uniqProducerName);
             }
             org.apache.pulsar.client.api.Producer<byte[]> producer = producerBuilder.create();
             logger.info("Create producer {} to topic {} , blockIfQueueFull is {},compressionType is {}", producer.getProducerName(),topic, blockIfQueueFull?"true":"false",compressionType);