most of our client major function require stack_id. We should
provide more specific information (at lest in function description)
to clearify that it's allowed to feed in stack name to `stack_id`
too. For example, both `heat.stacks.get($Stack_UUID)` and
`heat.stacks.get($Stack_Name)` works.
Change-Id: I4428097140e0391a77679f5c69e00966f249efd7