Fix duplicate vname problem. Instead of silently picking something else for them, fail if they try to use the same vname for two nodes in the expt.
Fix duplicate vname problem. Instead of silently picking something else
for them, fail if they try to use the same vname for two nodes in the expt.

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