58 commits since RC5. Highlights:

  - barebone ships get-serial-number, so every variant can identify itself
    to the test rig before it is written to
  - simpledrm display work: no display detected is reported as such, and the
    boot script no longer clears the serial console on a panel-less board
  - ustreamer starts from the camera rather than multi-user.target, and for a
    camera already attached at boot
  - autohotspot survives a dongle swap and leaves quietly with no wifi device
  - first-run releases the boot pin on failure and stays non-fatal under
    pipefail
  - DRAM frequency scaling disabled on A5 and A6
  - one SSH host key pair per board, not one per image