Use 'real' account fullnames when generating courses

The tool to generate test courses creates a bunch of users whose fullname always is "Test course user x". The lastname being the X.

I think it would be more useful to use real names, such as the ones generated by the data generator. Especially when you have to test sorting, or simply because it looks more like a real course. This could even be extended to the rest of the data generated by the plugin.

To keep in mind: It might be useful to be able to guess the user login from the fullname.