Tighten permissions on Etherpad settings file

The file in which our Etherpad settings reside is templated with
sensitive data like an API key and DB password. Remove the world
readable bit from it, and also drop user/group write perms while
we're at it.

Change-Id: I65b70237b4bc8f4e63aa0b717702c124e01ed777

playbooks/roles/etherpad/tasks/main.yaml

@@ -89,6 +89,7 @@
   template:
     src: settings.json.j2
     dest: /etc/etherpad/settings.json
+    mode: '0440'
 
 - name: Clean up from old ep_headings hack
   file: