Comment 9 for bug 1009294

My testing implies that the fix I've committed to the build scripts [1] will resolve this issue.
Heres what I did to test:
 * ran 3 instances of ami-a29943cb (us-east-1 ebs/ubuntu-precise-12.04-amd64-server-20120424)
    a.) control instance [verified config-changed prompt]
          apt-get update && apt-get install grub-pc
    b.) no user-data instance
          DEBIAN_FRONTEND=noninteractive dpkg-reconfigure grub-pc
          apt-get update && apt-get install grub-pc
          # verified no grub prompt
     c.) user-data that disabled running of grub-dpkg module in cloud-init
          DEBIAN_FRONTEND=noninteractive dpkg-reconfigure grub-pc
          sudo cloud-init-cfg grub_dpkg
          apt-get update && apt-get install grub-pc
          # verified no grub prompt

'c' was necessary above, because cloud-init modifies debconf preseed values in grub on first boot. I was concerned that having run 'dpkg-reconfigure grub-pc' in the build process, then booting and having cloud-init modify some portion of grub-pc debconf, then upgrading could cause a similar issue. It did not.

After we get images built with this change in them, we can verify that the issue is fixed by:
 * launching an instance of quantal or precise with serial > 20120607
 * adding a repository with a grub update (possibly a ppa with just a grub rebuild)
 * apt-get update
 * apt-get install grub-pc

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[1] http://bazaar.launchpad.net/~ubuntu-on-ec2/vmbuilder/automated-ec2-builds/revision/485