Revert "nsqd: healthy flag"

This reverts commit babf8ea3b68d7e75704073395b72c3f648c33409.
bump v0.2.30 stable
Revert "Revert "nsqd: healthy flag""

This reverts commit 49dedf5495721949d2a29751146850b465f4ee36.
nsqlookupd: move registrationdb to util
nsqd: use Serf for gossip
registrationdb: consolidate Producer and PeerInfo
wip rebroadcast