Set legacy_kafka_client_enabled = False on default

We change the default value of kafka_common.legacy_kafka_client_enabled
from True to False. The use of new Confluent Kafka client is
recommended.

Change-Id: I300958e1e945e5236b01f4e50cb01c18468cc524
Story: 2007924
Task: 40340

monasca_persister/conf/kafka_common.py

@@ -48,7 +48,7 @@ kafka_common_opts = [
                      'kafka-python library is used. Message format version '
                      'for the brokers should be set to 0.9.0.0 to avoid '
                      'performance issues until all consumers are upgraded.',
-                default=True)
+                default=False)
 ]
 
 kafka_common_group = cfg.OptGroup(name='kafka',

releasenotes/notes/disable-legacy-kafka-client-ff7181b387aaf536.yaml

@@ -0,0 +1,6 @@
+---
+upgrade:
+  - |
+    The default value of ``kafka_common.legacy_kafka_client_enabled`` has
+    changed from ``True`` to ``False``. The use of new Confluent Kafka
+    client is recommended.