Force EMULAB_MCADDR to always be a /8.  This is the easiest, least painful way forward for my life.
Force EMULAB_MCADDR to always be a /8.  This is the easiest, least painful
way forward for my life.

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