Implement prefect in Cluster so a node can start http listener in a
restricted mode.
Adjust tests; particularly start test.Holder in state Normal.
TODO:
- [ ] fix test TestMain_SendReceiveMessage
- [ ] add additional tests for `nodeState`
interfaces are in broadcast.go and http implementations in messenger.go (gossip
is already in a separate package). Next changes will bring in the HTTP nodestate
implementation, and separate the http implementation into a separate package.
GossipNodeSet and GossipBroadcaster had a lot of cross dependency - I made them
the same object and had it implement all three interfaces (NodeSet, Broadcaster,
BroadcastReceiver).
I implmented an HTTPBroadcastReceiver which runs as as separate server.
BroadcastReceiver is a separate entity on the pilosa.Server object and is
started separately from broadcaster and nodeset. In the case of GossipNodeSet,
the broadcast receiver must be started before Open()ing the Nodeset, because it
doesn't actually start listening until Open() is called, but it needs the
handler set up before then.
server/server.go was heavily refactored to configure the new structs and
interfaces on the pilosa.Server object.
