Release version names are easier for template authors to remember than
seemingly arbitrary dates. It should also make it clearer to new Heat
users that heat_template_version is not like a BIND zone file version
(which would be incremented with each version of the template).
Change-Id: Iae9b6a676702b2a115b18fdfb1ab2afbe5faacde
blueprint support-alias-for-heat-template-version-names