--iso and updates

[wgwoods]

When users upgrade from an iso, we don't enable the network. Sure, you can do fedup --iso --network 20 but this confuses people. Plus It makes more sense for the default case to be "upgrade system including updates", but to allow the user to turn off updates (if needed).

That's closer to the anaconda behavior, and it's safer too.

To do this, we'll need some way of examining the .iso to determine its version, and then we can use that version in the implicit --network VERSION