Add lost roles field in octavia

* the roles field is lost when implementing. This patch adds the field
* add enable_octavia example in globas.yml file

Change-Id: I94c33f78afafc903779c9f3bdb051fca39206211
Implements: blueprint octavia-ansible-role

ansible/site.yml

@@ -494,3 +494,7 @@
     - octavia-housekeeping
     - octavia-worker
   serial: '{{ serial|default("0") }}'
+  roles:
+    - { role: octavia,
+        tags: octavia,
+        when: enable_octavia | bool }

etc/kolla/globals.yml

@@ -149,6 +149,7 @@ kolla_internal_vip_address: "10.10.10.254"
 #enable_neutron_qos: "no"
 #enable_neutron_agent_ha: "no"
 #enable_neutron_vpnaas: "no"
+#enable_octavia: "no"
 #enable_rally: "no"
 #enable_sahara: "no"
 #enable_searchlight: "no"