dokku-alt/dokku-alt — pull request #10 by rikur (2014-08-09 22:55:34+00:00)
Title: Try to get rid of Grub GUI prompt that breaks installation on ubuntu-trusty-14.04-amd64-server-20140607.1 (ami-e7b8c0d7)

I just tested this with the AMI in the title and the installation was a breeze!

Source, with some modifications:
http://askubuntu.com/questions/146921/how-do-i-apt-get-y-dist-upgrade-without-a-grub-config-prompt