Fixes tags and when conditional for HAProxy

A missing comma after the second tag prevented the when conditional
from being evaluated correctly.

Change-Id: Ic18462212452a22ad556bed114e0a99440abe1ff
Closes-Bug: #1481130

ansible/site.yml

 ---
 - hosts: haproxy
   roles:
-    - { role: haproxy, tags: haproxy, keepalived when: enable_haproxy | bool }
+    - { role: haproxy, tags: haproxy, keepalived, when: enable_haproxy | bool }
 
 - hosts: mariadb
   roles: