Stack instance identifier property

The identifier property formats the stack name and ID for
REST API request paths.

This has the following consequences for each action method:
- get, same behaviour but using the identifier property
- delete, using the full identifier avoids one http redirect
- update, this method was non-functional before this change, and is
  now fixed

Change-Id: Ib2b12826243e25772acccb8ca56039e54d3857d5
Merge "Stack instance identifier property"