Get the ID for the current deployed overcloud stack if it exists.

def _get_stack(self, orchestration_client, stack_name):
        """Get the ID for the current deployed overcloud stack if it exists."""

        try:
            stack = orchestration_client.stacks.get(stack_name)
            self.log.info("Stack found, will be doing a stack update")
            return stack
        except HTTPNotFound:
            self.log.info("No stack found, will be doing a stack create")