Set correct mode for Koschei config

Koschei config contains some sensitive information, like DB password,
so it shouldn't be world-readable.

roles/koschei/tasks/main.yml

@@ -10,6 +10,9 @@
   template: >
     src="config.cfg.j2"
     dest="/etc/koschei/config.cfg"
+    owner=koschei
+    group=koschei
+    mode=0400
   notify:
   - restart koschei-polling
   - restart koschei-resolver