Trigger pipeline broken since artifacts can no longer be downloaded from URLs using PAT

We no longer permit artifacts to be downloaded (via CLI) using a PAT. Context: https://gitlab.com/gitlab-org/gitlab-ce/issues/50319 and internal slack discussion - https://gitlab.slack.com/archives/C02PF508L/p1543416106950600

We need to update our logic to use API to get the package from package building stage, not the web URL.