Implement rSTP / EdgePort / Portfast validation

[craiganderson]

It would be ideal to have a way to validate that switches have been configured properly to bring ports up to a forwarding state quickly (set with rapid STP, edgeport, or portfast settings depending on the switch vendor), rather than the 30 second default. The latter will cause PXE boot attempts to timeout.

There may not be a way of automating this validation for all nodes (PXE-boot chicken-and-egg issue here). At a minimum it would be possible to perform an interface down/up test in genesis.sh to validate that the port comes back up within a couple of seconds for this one node.