Add setting to override rabbitmq tcp connection backlog

Added RabbitTCPBacklog to allow overriding the connection
backlog for RabbitMQ. The current limit is set to 4096, but in
some scenarios with larger deployments this may be insufficient.

Change-Id: Ibcab8c20a4effcf64932d2fb7e3ed2354012f5f3

deployment/rabbitmq/rabbitmq-container-puppet.yaml

@@ -55,6 +55,10 @@ parameters:
     default: 65536
     description: Configures RabbitMQ FD limit
     type: number
+  RabbitTCPBacklog:
+    default: 4096
+    description: Configures RabbitMQ maximum TCP Backlog
+    type: number
   RabbitIPv6:
     default: false
     description: Enable IPv6 in RabbitMQ
@@ -143,7 +147,7 @@ outputs:
             rabbitmq::wipe_db_on_cookie_change: true
             rabbitmq::port: 5672
             rabbitmq::loopback_users: []
-            rabbitmq::tcp_backlog: 4096
+            rabbitmq::tcp_backlog: {get_param: RabbitTCPBacklog}
             rabbitmq::package_provider: yum
             rabbitmq::package_source: undef
             rabbitmq::repos_ensure: false

releasenotes/notes/releasenotes/notes/add_params_to_configure_rabbitmq_backlog-68da3a07ef506f57.yaml

@@ -0,0 +1,7 @@
+---
+other:
+  - |
+    A new parameter called ``RabbitTCPBacklog`` that specifies the maximum tcp
+    backlog for RabbitMQ as been added. The value defaults to 4096 to match
+    previous behavior and can be modified for the needs of larger scale
+    deployments by operators.