Add misc partition, identify root by PARTUUID

- Add back the misc partiton: fastboot stores boot data here for stuff
like reboot-bootloader
- Update kernel cmdline and fstab to mount / by GPT PARTUUID: now we
should be able to move that partition around freely, as needed.

Change-Id: If24c293671dbefda008184684f46e6796357296a
4 files changed