This change adds a test framework for the "eth" protocol and some basic
tests. The tests can be run using the './devp2p rlpx eth-test' command.
# Conflicts:
# core/forkid/forkid.go
# eth/discovery.go
# eth/handler.go
# eth/helper_test.go
# eth/protocol_test.go
* node: expose config in service context
* eth: integrate p2p/dnsdisc
* cmd/geth: add some DNS flags
* eth: remove DNS URLs
* cmd/utils: configure DNS names for testnets
* params: update DNS URLs
* cmd/geth: configure mainnet DNS
* cmd/utils: rename DNS flag and fix flag processing
* cmd/utils: remove debug print
* node: fix test