Add a spec for a heat datasource driver
Add a spec for a heat datasource driver

Blueprint:
  https://blueprints.launchpad.net/congress/+spec/heat-datasource-driver

Change-Id: I78feeaab14a7718884c10b64c4096eabddb16820

openstack/congress-specs,zhang935602068/congress-specs,ekcs/congress-specs