Some changes to listVlans to make it work with switch firmware version 2.70 .  The new code will be compatible with the old firware version (2.42), and should be slighly faster.
Some changes to listVlans to make it work with switch firmware version
2.70 .  The new code will be compatible with the old firware version
(2.42), and should be slighly faster.

Also fixed some return values, so that they don't appear to have failed
when they actually succeeded.

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