Name network interfaces according to vnode config

[eduble]

If we type for instance walt node config vnode1 networks=walt-net,exp-net, then it would be handy to have the network interfaces automatically named walt-net, exp-net inside the virtual node. Or if naming is too difficult, they could have an "altname" (ip link property add altname walt-net dev ens3, if iproute2 is new enough).
The association between mac and name could be passed using the kernel command line and then interpreted by walt-init or by some later code of the OS image (/bin/on-bootup, specific service, etc.).

[eduble]

With the new code being developped for handling a network-persistent boot mode, in a near future we'll have a standard way to pass node config options to walt-init scripts, thanks to the new script walt-fetch-node-config and the FetchNodeConfigHandler class on server side.