testing. Changes include:

* syncvlans option that compares the switches and the DB and makes
  everything consistent, including creating backing DB objects for the
  dozens of hand created vlans, since all vlans must have a DB object
  so that vlan tag reservations can be consistent across all stacks.

* Clean up the tag stuff a bit. No longer store tag in the
  lan_attributes table since that is a transient table, prone to
  getting out of sync with reality.

* Changes to how the set of devices in a stack is chosen; ensure that
  we do not reference switches that are not needed (no ports on that
  switch and does not traverse a trunk on that switch). This should
  allow us to move the Backbone switches back into the Experimental
  stack, without fear that normal swapin will block cause the long
  distance links to those switches is down.