engine : stack_resource change state_description to status_reason

The internal API changed this name recently, but this got missed
due to lack of test coverage for this exception.  Turns out adding
that test coverage is really hard due to all the coroutine magic,
so we'll have to fix that at some later time.

Change-Id: I98a0c5bb8f3f001a7d215bcdf64cad841e42ef85
Merge "engine : stack_resource change state_description to status_reason"