Allow better user experience with CD-ROM hotswapping

[msmuenchen]

At the moment, UTM when trying to install the guest tools will give an error "no free cd/rom device" when selecting the "install guest utils" option if the setup ISO is still mounted.

UTM should offer to unmount / "eject" the current CD-ROM image and swap it for the guest tools image instead of the user having to manually eject it.

[ideologysec]

or just add a second CD-ROM device? there's no reason I'm aware of that you can't have multiples.