Neutron configuration validation

[lukego]

We should validate configuration parameters and have commands like net-create and net-update report errors.

For example, if an L2TPv3 parameter has a bad value (e.g. invalid IP address) this should be an error, and so should an unrecognized parameter name in binding:profile. This kind of error should be caught on the Neutron server without pushing the configuration into the database and traffic node.

We should also have a way to override validation. This would be useful in situations where the traffic process supports more options than the Neutron server e.g. if the operator has upgraded the traffic process with new features but (for whatever reason) does not immediately update the neutron server. Perhaps the operator could supply validate=false as a binding:profile attribute to suppress error checking.

@N-Nikolaev

[lukego]

(Oops: more relevant commands would be port-create and port-update.)