Run an "apt-get update" before trying to install packages.

Otherwise Vagrant shows 404s.

roles/ispmail-packages/tasks/main.yml

@@ -1,6 +1,6 @@
 ---
 - name: install required binary packages
-  apt: name={{item}} state=installed
+  apt: name={{item}} state=installed update_cache=yes
   with_items:
   - mysql-server
   - postfix