[Merge] ~rcj/livecd-rootfs/+git/livecd-rootfs:test/binary_build_mirrors-bionic into livecd-rootfs:ubuntu/bionic

[Robert C Jennings]

Feedback on IRC from cjwatson and vorlon was positive, it confirmed that this is a decent path to take.
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https://code.launchpad.net/~rcj/livecd-rootfs/+git/livecd-rootfs/+merge/380853
Your team Ubuntu Core Development Team is requested to review the proposed merge of ~rcj/livecd-rootfs/+git/livecd-rootfs:test/binary_build_mirrors-bionic into livecd-rootfs:ubuntu/bionic.