First past at integration of VLAN firewall:

1. Do all the magic snmpit-speak at the beginning of a swapin.

2. Undo all the magic snmpit-speak right before nfree in a swapout.
   THIS IS CURRENTLY UNSAFE because I don't yet put all the firewalled
   nodes into "purgatory" before dropping the firewall.  That is yet
   to come.

3. Disallow modification of a firewalled experiment til I figure out
   how to do it safely.