Add basic read-only tests for heat cli

Adds some smoke-tests for the heat CLI interface, similar to what
exists for other projects - it's not an exhaustive test but it
provides coverage of the interfaces which do not require content
to be created or modified.

Change-Id: I9921815bfb17fbe4d010d41e2a79a8d9b292271d
blueprint: tempest-heat-integration
Merge "Add basic read-only tests for heat cli"