Interactive address selection

[masnax]

Closes #76

Now shows a table of addresses and their interfaces on the local machine. The user's selection will be used as the listen address and to lookup peers.

After this step, the user will be prompted with a binary yes/no for whether or not to filter on the subnet of the listen address.

• If --address is given, that will be used in lieu of the interactive step.
• If --auto, the first address will be used and peer lookup will be limited to its subnet.
• If only one address is available, the interactive step will be skipped and we will go right to asking for subnet filtering.
• The --subnet flag is gone now

---

Additionally, in response to the comments in #74, if there are too few disks for distributed storage after selecting local storage, the distributed storage selection step will be entirely skipped with a warning about insufficient disks, rather than prompting the user to add disks as normal.

[stgraber]

Can we get the CIDR from the address instead of assuming /24 for v4 and /64 for v6 as that can be very wrong?

I'd probably have gone with net.InterfaceAddrs() which gets you CIDR of all addresses on the system.
You'd then need to filter our anything that's not a global address from that by using ip.ParseIP and only going for GlobalUnicast.

[stgraber]

	addrs, err := net.InterfaceAddrs()
	if err != nil {
		os.Exit(1)
	}

	for _, addr := range addrs {
		ip, _, err := net.ParseCIDR(addr.String())
		if err != nil {
			continue
		}

		if !ip.IsGlobalUnicast() {
			continue
		}

		fmt.Printf("%s\n", addr.String())
	}

[masnax]

Yeah that's a good point. I was less concerned about invalid subnets since I had added the --subnet flag, but since that's gone it can be problematic.

I've added a Subnet field to the NetworkInfo struct now. So any selected address will have its associated subnet be used. If the user specifies their own address with --address, init will fail if that address doesn't fit in any of the found subnets.