[Merge] ~mwhudson/livecd-rootfs/+git/livecd-rootfs:tpm-seed-in-live-layer into livecd-rootfs:ubuntu/master

[Michael Hudson-Doyle]

The reason this saves space is because the TPM FDE model is currently duplicated between the minimal and full layers. The idea yes is that snapd will copy the system to the installed system when we call its "install" API.

This is also a good idea when snap components come into view, as we will be able to direct snapd on which components to install on the target system.
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https://code.launchpad.net/~mwhudson/livecd-rootfs/+git/livecd-rootfs/+merge/466202
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