DNS errors

Near the end of the image build, we try to run "apt-get update" once again in the image, with the correct mirror for the image:

+ chroot /tmp/tmpVxZuTf apt-get update
Err:1 http://httpredir.debian.org/debian unstable InRelease
  Could not resolve 'httpredir.debian.org'
Reading package lists... Done
W: Failed to fetch http://httpredir.debian.org/debian/dists/unstable/InRelease  Could not resolve 'httpredir.debian.org'
W: Some index files failed to download. They have been ignored, or old ones used instead.

This seems to be only a minor issue, in that it doesn't cause the build to fail or have any major problems.