Our discovery crawler spits out a huge amount of logs, most of which is pretty non-interesting. This change moves the very verbose output to Debug, and adds a 8-second status log message giving the general idea about what's going on.
This adds an implementation of the current discovery v5 spec.
There is full integration with cmd/devp2p and enode.Iterator in this
version. In theory we could enable the new protocol as a replacement of
discovery v4 at any time. In practice, there will likely be a few more
changes to the spec and implementation before this can happen.
