Support namespacing RabbitMQ logs

The RabbitMQ role supports namespacing the service via the
project_name. For example, if you change the project_name, the
container name and config directory will be renamed accordingly. However
the log folder is currently fixed, even though the service tries to
write to one named after the project_name. This change fixes that.

Whilst you might generally use vhosts, running multiple RabbitMQ
services on a single node is useful at the very least for testing,
or for running 'outward RabbitMQ' on the same node.

This change is part of the work to support Cells v2.

Partially Implements: blueprint support-nova-cells
Change-Id: Ied2c24c01571327ea532ba0aaf2fc5e89de8e1fb

ansible/roles/rabbitmq/templates/rabbitmq.json.j2

@@ -27,7 +27,7 @@
             "recurse": true
         },
         {
-            "path": "/var/log/kolla/rabbitmq",
+            "path": "/var/log/kolla/{{ project_name }}",
             "owner": "rabbitmq:rabbitmq",
             "recurse": true
         }