This commit converts all the uses of wgkey to the new key interfaces.
It now has specific machine, node and discovery keys and we now should
use them correctly.
Please note the new logic which strips a key prefix (in utils.go) that
is now standard inside tailscale.
In theory we could put it in the database, but to preserve backwards
compatibility and not spend a lot of resources on accounting for both,
we just strip them.
This commit changes the way CLI and grpc-gateway communicates with the
gRPC backend to socket, instead of localhost. Unauthenticated access now
goes on the socket, while the network interface will require API key (in
the future).
This commit reworks getAvailableIp with a "simpler" version that will
look for the first available IP address in our IP Prefix.
There is a couple of ideas behind this:
* Make the host IPs reasonably predictable and in within similar
subnets, which should simplify ACLs for subnets
* The code is not random, but deterministic so we can have tests
* The code is a bit more understandable (no bit shift magic)
This commit makes the IP prefix used to generate addresses configurable
to users. This can be useful if you would like to use a smaller range or
if your current setup is overlapping with the current range.
The current range is left as a default
