Having the same issue (same log data for us.archive.ubuntu.com with Trusty) as the OP with MAAS, I executed: sed -i '@s@mirror@choose-mirror@g' /etc/maas/preseeds/generic
which resolved the issue.
Having the same issue (same log data for us.archive. ubuntu. com with Trusty) as the OP with MAAS, I executed: choose- mirror@ g' /etc/maas/ preseeds/ generic
sed -i '@s@mirror@
which resolved the issue.