Support deploying storm worker and storm nimbus separately

This allows storm worker and nimbus services to be deployed on
separate hosts.

Change-Id: Icb990d289fbfb4d8f782c255fc50d092964384f7

ansible/site.yml

@@ -518,7 +518,9 @@
         when: enable_kafka | bool }
 
 - name: Apply role storm
-  hosts: storm
+  hosts:
+    - storm-worker
+    - storm-nimbus
   serial: '{{ kolla_serial|default("0") }}'
   roles:
     - { role: storm,