Code review comment for ubuntu-archive-tools:update-output-helper

How I'm trying to use it:

$ update-output-helper $(wcat https://ubuntu-archive-team.ubuntu.com/proposed-migration/update_output.txt | sed -n -e'/[[:space:]]perl[[:space:]]/ { s/^trying: //p }' | head -n1)
$ chdist -d "/home/vorlon/.cache/brapt" apt u-a-h --dry-run install accerciser

and this succeeds where, based on update_output, I expect it to fail.