Use dest instead of src for get_url downloaded resource
Use dest instead of src for get_url downloaded resource

'src' is a temporary file reference that exists only for the
duration of the download, it is not the location where the file
gets downloaded.

The location of the downloaded file is the 'dest' key, so use that
instead.

Change-Id: I2ff1b9c442d1cc88820c49d680567b0b16401ef3

openstack-infra/openstack-zuul-jobs,openstack-infra/openstack-zuul-jobs