Curl to redo the request (Found 302)

The URL to download the Fedora 19 images is not persistent anymore,
they are now download from http://download.fedoraproject.org where the
request will be redirected to a different location. Passing the -L option
to the curl command will make it redo the request on the new place and
download the image correctly.

Related to bug #1199237

Change-Id: Ib9b9d65734992e2bf1a6888c5f2eb9de366f8204