Refactoring of _heat_settings.py

define openstack_heat_stack as dict
example of pillar data:

  horizon:
    server:
      version: mitaka
      openstack_heat_stack:
        enable_user_pass: false

Change-Id: Ibb5e713af0e635cb9a6f23b5f3197c37f2986bc9
diff --git a/horizon/files/horizon_settings/_heat_settings.py b/horizon/files/horizon_settings/_heat_settings.py
index acb4a71..84fa80c 100644
--- a/horizon/files/horizon_settings/_heat_settings.py
+++ b/horizon/files/horizon_settings/_heat_settings.py
@@ -7,5 +7,9 @@
 {%- endif %}
 
 {% if app.openstack_heat_stack is defined %}
-OPENSTACK_HEAT_STACK = {'enable_user_pass': {% if app.openstack_heat_stack %}True{% else %}False{% endif %}}
+OPENSTACK_HEAT_STACK = {
+{%- for key, value in app.openstack_heat_stack.iteritems() %}
+    "{{ key }}": {{ value }}{% if not loop.last %},{% endif %}
+{%- endfor %}
+}
 {%- endif %}