Wipe auto-generated SSL certificates during setup and re-create them at startup.

This is to address the issue of installation-unique data
making it to the image.
Introduce code that changes rootfs and swap UUIDs at first boot.

update-uuids script is the heavy lifter, it operates in either of
two modes:
(1) auto mode (when called w/o arguments and if /.h-update-uuids exists)
    -- which creates and sets new random UUIDs and
(2) manual mode (when called with exactly two arguments: first one being
    new rootfs UUID, second one being new swap UUID) -- sets specified
    UUIDs

As update-uuids runs after swap has been turned off, swap device
is conveyed to it using SWAPDEV variable.

At fist boot, swaps must be turned on for update-uuids to operate -- add that
to the list of prerequisites.

Also use predefined UUIDs during setup (for troubleshooting).