nodes are treated specially. For inner boss/ops, ignore most of what
DHCPD returns; we need to do the DHCP so that we know what interface,
but for the moment stuff is hardwired into /etc/rc.conf when the inner
boss and ops are created. I can probably fix this up later as needed,
to be more dynamic for supporting swapout/swapin of an inner emulab,
but swapout and restore of an inner elab has som many open issues,
that not worrying about it now.

For inner nodes, the change is simple; If no hostname provided, ignore
the DHCPD reply completely, favoring a full reply from the inner
control network, and returning -1 from the exit hook so that dhclient
keeps trying in the foreground.

I am committing these so they get into new images.