This patch fixes problems found in api-ref documentation related
to stack actions and missing stack APIs. More specifically, this
include the following changes:
- Fix status code documentation about stack actions;
- Added response parameters for some actions although there is no
body returned -- there are still header returned;
- Added documentation about stack-export API;
- Added documentation about stack-environment-show API;
- Added documentation about stack-files-show API;
Change-Id: I8b2266ec7a7a22fc1cb1782e98beac315e054013