This patch updates heatclient so that it supports creating
stacks from an object (Swift container) which contain nested
stack relative links to nested stack URLs.
The motivation here:
We would like to be able to use heatclient to create stacks directly
from Swift containers in TripleO. The --template-object support already
exists and is great... it just needs to support loading the associated
nested stacks as well.
Change-Id: I53ac83e9f9985224d19993935467c03611aaef6a
Closes-bug: #1532326