SDR nodes (type=sdr, but this applies to other similar types) are in the
"pc" class, but really they are not pcs, they are more like blackboxes
that can be power cycled and are always ISUP.

So, I added a "sdr" package to libossetup, that basically just does a
power cycle to put them into a known state, and makes sure the
eventstate is ISUP.

I added "blackbox" to the sdr type definition. Aside; when something is
a blackbox, we should bypass all image/osinfo handling, but that's a
tale for another day.

I added a isblackbox() check in power, to skip any eventstate
handling. Aside; node_reboot should possibly skip right to power cycle
for blackbox nodes, instead of trying to ping it or ssh into it.