move call to update_templates on service startup into a django-admin command

cms/djangoapps/contentstore/__init__.py

-from xmodule.templates import update_templates
 
-update_templates()

rakefile

@@ -441,6 +441,13 @@ namespace :cms do
 end
 
 namespace :cms do
+  desc "Imports all the templates from the code pack"
+  task :update_templates do
+    sh(django_admin(:cms, :dev, :update_templates))
+  end
+end
+
+namespace :cms do
   desc "Import course data within the given DATA_DIR variable"
   task :xlint do
     if ENV['DATA_DIR'] and ENV['COURSE_DIR']