This is the last remaining area of the code where we were slinging around
CloudFormation-formatted snippets of template. Replace it with a proper API
along the lines of ResourceDefinition.
The default implementation of the new template.Template.outputs() method is
equivalent to what we have previously done spread throughout the code, so
that third-party Template plugins will not be affected until they have had
time to write their own custom implementations.
Change-Id: Ib65dad6db55ae5dafab473bebba67e841ca9a984