AC-752 Add RabbitMQ role to setup, update CONTRIBUTING doc.

awx/settings/local_settings.py.example

@@ -43,6 +43,9 @@ if len(sys.argv) >= 2 and sys.argv[1] == 'test':
         }
     }
 
+# Celery AMQP configuration.
+BROKER_URL = 'amqp://awx-dev:AWXsome1@localhost:5672/awx-dev'
+
 # Absolute filesystem path to the directory to host projects (with playbooks).
 # This directory should NOT be web-accessible.
 PROJECTS_ROOT = os.path.join(BASE_DIR, 'projects')