Bug Fix; cull out duplicates in RecordVlanInsertion so that the members list of vlans table does not get messed up.
Bug Fix; cull out duplicates in RecordVlanInsertion so that the
members list of vlans table does not get messed up.

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