Unattended grub configuration after kernel upgrade

Today I have been working on automatic deployment of an ubuntu server. I got stuck on automatic updating of the server using apt-get upgrade trying to upgrade to a new kernel. The log looks like this:

Setting up linux-image-3.2.0-24-generic (3.2.0-24.39) ...
Testing for an existing GRUB menu.lst file ... found: /boot/grub/menu.lst
(...)

Then a question is presented:

Package configuration

    ┌─────────────────────────────────┤  ├─────────────────────────────────┐    
    │ A new version of /boot/grub/menu.lst is available, but the version   │    
    │ installed currently has been locally modified.                       │    
    │                                                                      │    
    │ What would you like to do about menu.lst?                            │    
    │                                                                      │    
    │      install the package maintainer's version                        │    
    │      keep the local version currently installed                      │    
    │      show the differences between the versions                       │    
    │      show a side-by-side difference between the versions             │    
    │      show a 3-way difference between available versions              │    
    │      do a 3-way merge between available versions (experimental)      │    
    │      start a new shell to examine the situation                      │    
    │                                                                      │    
    │                                                                      │    
    │                                <Ok>                                  │    
    │                                                                      │    
    └──────────────────────────────────────────────────────────────────────┘    

The desired outcome would be to select the first option and to continue:

Replacing config file /run/grub/menu.lst with new version
Updating /boot/grub/menu.lst ... done

After running the upgrade by hand, I used debconf-get-selections to inspect the correct answer for the question (see other settings). It seems like update_grub_changeprompt_threeway is the question that should be answered. However, setting this using debconf-set-selections presented me with the same question:

debconf-set-selections <<< "grub grub/update_grub_changeprompt_threeway select install_new"
apt-get -y dist-upgrade

How can this question be automated?

I was able to get around this by using export DEBIAN_FRONTEND=noninteractive, before running apt-get upgrade -y.

On Ubuntu 16.04, this sequence should avoid the interactive dialog:

export DEBIAN_FRONTEND=noninteractive
apt-get update
apt-get upgrade -yq

Note that the -q flag is important.

(Reference: This question on devops)