[Merge] ~mwhudson/livecd-rootfs/+git/livecd-rootfs:netboot-fixes into livecd-rootfs:ubuntu/master

[Michael Hudson-Doyle]

FWIW I'm still confused about what is possible here. grub seems to want to set its prefix to an absolute /grub on the tftp or http server which might make multi-arch support difficult :( (and unless I'm confused -- definitely possible -- PXE and HTTP boot seem to differ in whether passing a relative path to grub's "linux" and "initrd" commands work).
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https://code.launchpad.net/~mwhudson/livecd-rootfs/+git/livecd-rootfs/+merge/426680
Your team Ubuntu Core Development Team is requested to review the proposed merge of ~mwhudson/livecd-rootfs/+git/livecd-rootfs:netboot-fixes into livecd-rootfs:ubuntu/master.