tests: Make iso-file.iso a real ISO file

Instead of an empty one. That's the first 1k of a Fedora 20
nightly image.
Add PC Engine, GameCube and Wii "ROM" types

The different types of Wii disc images are merged into one, as
there's likely no difference between support one and all for the
majority of applications.

Magic for Wii and GameCube images from:
http://wit.wiimm.de/download/magic.txt