Add support for overriding params from environment

If a matching environment variable is found, then the value will be
replaced when generating the output from the template.  This matching
occurs both on the parameter name in uppercase (NOTIFICATION_INTERVAL)
or the resource name + the parameter name (HOST_NOTIFICATION_INTERVAL)

Author: Clayton O'Neill

examples/nagios_.jinja2

@@ -8,13 +8,20 @@ define {{object_name}} {
     {{object_name}}_name {{resource.name}}
     {% endif %}
     {% for key,value in resource.parameters.items() %}
+    {% set name_key = (object_name ~ '_' ~ key)|upper %}
     {% if key not in metaparams or key in allowed_metaparams %}
     {% if value is iterable and value is not string %}
     {{key}} {{value|join(", ")}}
     {% else %}
+    {% if name_key in env %}
+    {{key}} {{env[name_key]}}
+    {% elif key|upper in env %}
+    {{key}} {{env[key|upper]}}
+    {% else %}
     {{key}} {{value}}
     {% endif %}
     {% endif %}
+    {% endif %}
     {% endfor %}
 }
 {% endfor %}

puppetdb_stencil.py

@@ -8,6 +8,7 @@
 
 import argparse
 import logging
+import os
 import pypuppetdb
 import jinja2
 
@@ -36,7 +37,8 @@ def render_resources(database, resource_type, template_names):
         LOG.error('No template found for {0}'.format(resource_type))
     else:
         return template.render(resource_type=resource_type,
-                               resources=resources, metaparams=METAPARAMS)
+                               resources=resources, metaparams=METAPARAMS,
+                               env=os.environ)
 
 
 def main():