Fix the std-x86 layout to produce a bootable system. Due to
limitations in mkimg we're still not quite to where I'd like to be
(I'd like to put s3 first on the disk, then s1, but mkimg won't allow
that currently). However, the resulting image now boots with qemu using:

qemu-system-x86_64 -hdd $file -serial telnet::4444,server -nographic

We'll need tweaks to create a specialized /etc/rc.d/growfs that can
create a properly grown image for either the simple or ping-pong
cases, but that will be later. Switched to pure serial console (-h)
instead of video or serial (-P) since that fits this usecase better.

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