Even after several reboots of the VM it still kept freezing at boot. Here's what I did to get them boot up to the login prompt:
- When powering on the VM press any button to get into the grub menu
- Press 'e' to edit the menu
- Select the second line starting with 'kernel' and press 'e' to edit this line
- At the end of the line after the 'quiet' add the parameter 'vga=normal'. [You can also use any other valid value for vga, e.g. 769 for 640x400 8 bit color or 791 for 1024x768 16bit color but normal is ok for a server install].
- Press 'enter' to save the changes
- Press 'b' to boot
Now the VM booted quickly up to the login prompt. And it did so after each reboot or power off/on.