Updates for designs/neutron/*

[eugeneia]

Amended neutron2snabb to handle updated Neutron CSV dump format. Includes support for L2TPv3 configuration from the Neutron side.

This adds lib.json:decode for parsing JSON strings. Credit is due to Craig Mason-Jones' JSON4Lua.

Also adds a smoketest for neutron2snabb to designs/neutron/selfest.sh.

More:

• Fixes a bug mentioned below ("only create configurations for local host").
• Implements atomic update-only-when-changed for neutron-sync-agent.
• Removes some obsolete configuration keys from neutron2snabb and lib.nfv.config (see nd_light for why remote_mac they became obsolete).

[eugeneia]

This will probably conflict with neutron2snabb egress filters, please merge that PR first then I will resolve the eventual conflicts.

[lukego]

We should do additional filtering somewhere here:
The database configuration includes records for every compute host (potentially hundreds) but we only want to generate config files for the local traffic processes on our node.

So we should have a check along the lines of:

if vif_details.zone_host == myhostname then
   ...
end

where myhostname is the unix host name of the machine.

[lukego]

There is a related feature that we should add, but I suspect it belongs in neutron-sync-agent and not directly in neutron2snabb:

The new configuration file for a traffic process should be created:

• Only if the configuration has changed. i.e. if the new file and the old file are the same then we should not bother the traffic process with an update.
• Atomically, so that the traffic process will never try to load a partly-written file.

I suspect both could be handled by updating the neutron-sync-agent script to generate files into a temporary location, then diff to see if there are changes compared with the running configuration, and if so do an atomic update with mv.