Allow heat on a dedicated node in a HA setup

Without this the haproxy role doesn't have the facts it needs to
render it's template, resulting in the following error:

TASK: [haproxy | Copying over config(s)]
************************************** fatal: [control01] => {'msg':
"AnsibleUndefinedVariable: One or more undefined variables: 'dict
object' has no attribute u'ansible_eno1'", 'failed': True}

This is similar to the fix applied previously for other services in
I99b7dbebd5a6193e192ee258ddf576d18db90ed7.

Change-Id: I279374e8861c02e3aa12988b885be7361e0cf2f5
Closes-Bug: 1524739

ansible/site.yml

@@ -18,6 +18,7 @@
     - nova-api
     - rabbitmq
     - swift-proxy-server
+    - heat-api
   roles:
     - { role: haproxy,
         tags: haproxy,