The UNCONFIGURED FSTAB warning was being left in the result, the discard
option wasn't included, and the fsck flag was 0 (all in marked contrast
to the preinstalled server images).
Changes in either livecd-rootfs or ubuntu-image seem to periodically
break the transfer of the pre-allocated swapfile (copying it in such a
fashion that it winds up "with holes" and thus unable to be used as a
swapfile). Rather than fight this, just use a simple systemd service to
generate the swapfile if it doesn't exist (using fallocate to keep
things snappy).
