Add option to show soft-deleted stacks in stack-list

A new boolean stack-list option, "--show-deleted", will cause
soft-deleted stacks to be included in the stack-list output.

Example:
  heat stack-list --show-deleted

Change-Id: I8ad6b4b477448000688bf83afe6b41ebf29656a4
blueprint: stack-list-soft-deleted
Merge "Add option to show soft-deleted stacks in stack-list"