Add ability to configure rabbitmq

As rabbitmq's configuration file is not ini or yaml file,
there is no option to extend configuration by new config
options via merge_configs or merge_yaml.

This patch moves config options to dictionary
so it can be overriden in /etc/kolla/globals.yml.

Change-Id: I5cd772f4fb80a0e200fb24d67be735ca81e3fdeb

ansible/roles/rabbitmq/defaults/main.yml

@@ -84,6 +84,7 @@ rabbitmq_server_additional_erl_args: "+S 2:2 +sbwt none +sbwtdcpu none +sbwtdio
 rabbitmq_tls_options: {}
 # To avoid split-brain
 rabbitmq_cluster_partition_handling: "pause_minority"
+rabbitmq_extra_config: {}
 
 ####################
 # Plugins

ansible/roles/rabbitmq/templates/rabbitmq.conf.j2

@@ -11,6 +11,9 @@ cluster_partition_handling = {{ rabbitmq_cluster_partition_handling }}
 management.listener.ip = {{ api_interface_address }}
 management.listener.port = {{ role_rabbitmq_management_port }}
 management.load_definitions = /etc/rabbitmq/definitions.json
+{% for key, value in rabbitmq_extra_config.items() %}
+{{ key }} = {{ value }}
+{% endfor %}
 
 cluster_formation.peer_discovery_backend = rabbit_peer_discovery_classic_config
 {% for host in groups[role_rabbitmq_groups] %}

releasenotes/notes/rabbitmq-configuration-6b100a390734dc29.yaml

+---
+features:
+  - |
+    Adds the ability to configure rabbitmq via ``rabbitmq_extra_config``
+    which can be overriden in globals.yml.