[Merge] ~dannf/livecd-rootfs/+git/livecd-rootfs:udevadm-lock into livecd-rootfs:ubuntu/master

[dann frazier]

DO NOT MERGE YET - this will definitely be broken until we backport this fix to udev:

https://github.com/systemd/systemd/commit/ba340e2a75a0a16031fcb7efa05cfd250e859f17

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https://code.launchpad.net/~dannf/livecd-rootfs/+git/livecd-rootfs/+merge/459549
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