Minor nits.  The most important: when selecting eligible node types from the DB, only select those for which a node of role 'testnode' exist.  This will eliminate the pc1500, where we only have a couple of tipservers of that type.
Minor nits.  The most important: when selecting eligible node types from the
DB, only select those for which a node of role 'testnode' exist.  This will
eliminate the pc1500, where we only have a couple of tipservers of that type.

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