graphite.wsgi : update for django 1.7

Django 1.8 in Xenial hits changes to the app loading made in 1.7 [1].
On Xenail and above, ship a slightly different wsgi loader that uses
the new-style loading.

[1] https://docs.djangoproject.com/en/dev/releases/1.7/#app-loading-changes

Change-Id: Ia741af25391603fe81c0185b586b5841910f714a

manifests/init.pp

@@ -259,9 +259,25 @@ class graphite(
     require => File['/etc/graphite'],
   }
 
+  # later versions of django require a different wsgi loader; swap it
+  # in here for > trusty
+  case $::operatingsystem {
+    'Ubuntu': {
+      if versioncmp($::operatingsystemrelease, '14.04') <= 0 {
+        $django_wsgi_template = 'graphite.wsgi.erb'
+      }
+      else {
+        $django_wsgi_template = 'graphite.wsgi.django17.erb'
+      }
+    }
+    default: {
+      fail('Platform not supported')
+    }
+  }
+
   file { '/etc/graphite/graphite.wsgi':
     mode    => '0444',
-    content => template('graphite/graphite.wsgi.erb'),
+    content => template("graphite/${django_wsgi_template}"),
     require => File['/etc/graphite'],
   }
 

templates/graphite.wsgi.django17.erb

@@ -0,0 +1,15 @@
+import os, sys
+sys.path.append('/var/lib/graphite/webapp')
+os.environ['DJANGO_SETTINGS_MODULE'] = 'graphite.settings'
+
+from django.core.wsgi import wsgi_application
+application = get_wsgi_application()
+
+# READ THIS
+# Initializing the search index can be very expensive, please include
+# the WSGIScriptImport directive pointing to this script in your vhost
+# config to ensure the index is preloaded before any requests are handed
+# to the process.
+from graphite.logger import log
+log.info("graphite.wsgi - pid %d - reloading search index" % os.getpid())
+import graphite.metrics.search