There was a question about preseeding 14.04.2 failing a while back

[Tom H]

On Thu, Jul 14, 2016 at 8:41 AM, Tom H <tomh0665 at gmail.com> wrote:
>
> I've deleted that email but, IIRC, it was about a message that grub
> wouldn't be installed.
>
> There was a change in d-i whereby you have to set
> "grub-pc/install_devices" and that's possibly the cause of the
> failure.

Or "grub-installer/choose_bootdev".