Check devices before downloading & extracting

[jjlawren]

If multiple USB devices are available, it's not discovered until the platform has already been downloaded and extracted. These files are not reused during subsequent runs and are downloaded again.

[laris]

95205cd

I remember it will report multi usb devices in this patch.

Maybe need a patch to keep the downloaded files?

[ahayes]

In my case the server is on a very slow and expensive satellite link and has a pair of USB keys for redundancy. It would be nice to be prompted which key to update and have the downloaded platform file saved.