Unit tests: Check for lost resource after failed rollback

Check that when a new resource is added to a stack during an update and it
is unable to be deleted during rollback, that we do not lose track of it
but rather it remains in the template whence we can later attempt again to
delete it.

Change-Id: I83ebbc16c84561b69f9bdb8e7485de85b695c1b8
Related-Bug: #1330016
Change help text for StructuredConfig.CONFIG property

Current help text 'serialized to the chosen format' is misleading
as it only converts to JSON. Hooks have the responsibility to
convert to the required format and use it.

Change-Id: Ic9df130193982c3a89330931812512e055a49029
Closes-Bug: #1339464
Merge "Unit tests: Check for lost resource after failed rollback"
Merge "Change help text for StructuredConfig.CONFIG property"