Fix plc ip by putting it first in the lan list.
Fix plc ip by putting it first in the lan list.

By default, limit plab node types to pc850 and pc2400c2 since they
won't boot on pc3000s and pc600 are not well tested.

nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome,nmc-probe/emulab-nome