Add request id to download path

This gets a request ID into the delivery path. It's an end-to-end change, so here's what you'll find:

• Add a a new --prefix argument to deliver you can supply to insert a path element
• Revise the workflow service to automatically add a workflow_request_id parameter to the user arguments during its template rendering process
• Migration to use the --prefix argument from the test_download workflow
• Vulture bug fix: split command line arguments properly on spaces

In manual testing, I verified that these changes work and propagate the workflow ID into the result URL