Switch to vmsvga for graphics controller

[sc68cal]

VirtualBox 6.0 shows an error about the settings for the graphics controller in the GUI, and there are also issues where the virtualbox machine hangs and does not finish booting. Changing to the vmsvga driver resolves this.

This probably fixes issues like #282

[jafingerhut]

Thanks for the suggested change. I tried it out on a Windows 10 Enterprise host system, running VirtualBox 6.1.36. It did result in a working VM. One difference I noted is that with the current unchanged Vagrantfile, I can change the Monitor Settings in the VM to 1024x768 and even some larger values. With these changes, I could only successfully change the monitor settings from the original 800x600 to the smaller 640x480, but not to 1024x768 or any larger settings.

If this experience is similar for others, I don't think I would want to limit users to those resolutions.

I agree that experiences like #282 are not good, but I have not experienced it myself, and have no personal way to test whether this change improves on it. Perhaps someone else can try out these changes who has experienced a problem like #282 and can say whether this change improves things for them.

[sc68cal]

That's odd because I was able to drag and resize the VM window dynamically to make it bigger or smaller and it changed the resolution to whatever the guest VM window size was