Purge remaining heat_keystoneclient v2 code

Removes the remaining v2 specific code, and converts the trust
handling code to use only the v3 client.

This completes the keystone-v3-only blueprint.

blueprint: keystone-v3-only
Change-Id: Iac5b7dd73f5827cc5247a3b71d63a0f5ea266628
Only update_and_save if the stack exists

The following error can happen during a stack-delete:

  AttributeError: 'NoneType' object has no attribute 'update_and_save'

Only update_and_save the stack if it is not None.

Change-Id: I8c27ed6a461c699eba7da5bef8e879f1c0bdaf6b
Closes-Bug: #1274664
Merge "Purge remaining heat_keystoneclient v2 code"
Merge "Only update_and_save if the stack exists"