StackResource set requires_deferred_auth=True

The dynamic evaluation of requires_deferred_auth will not work
as the nested stack has not been created when requires_deferred_auth
is evaluated.

In some cases subclasses of StackResource could implement dynamic
evaluation but for now it is safer to assume any template with a
nested stack needs requires_deferred_auth=True

Change-Id: I4ca3804ede5c7aa2167931279e5bed84480ac454
Closes-Bug: #1229412
Improve test coverage of stack deletion

Adding tests to cover stack deletion timeout, stack deletion
failure and also to cover check_delete_complete.

Fixes bug #1220723

Change-Id: I50dbaf37f6d95b731e8496aa90c6c6e5bcc27ab1
Merge "StackResource set requires_deferred_auth=True"
Merge "Improve test coverage of stack deletion"