RFC: nff-go in Azure with failsafe

[darinkes]

For example:

config := flow.Config{
	DPDKArgs: []string {
		"--vdev=net_vdev_netvsc0,iface=eth1",
		"--vdev=net_vdev_netvsc1,iface=eth2",
	},
}
flow.CheckFatal(flow.SystemInit(&config))

Closes #688