Switch to heat_template_version: 2013-05-23

To support underclouds and seeds running older than the very
latest heat.

2013-05-23 lacks function list_join, so this change reverts to
using the equivalent function Fn::Join.

Change-Id: I039f57ab39c1fcfc319a7a34265ba4fabf4ccd08
Closes-Bug: #1354305