refactor handler Close func to use errgroup to be a bit less messy.
refactor pilosa.Server closing to actually return an underlying error if one occurs
add option to pilosa/test.Cluster and pilosa/server.Command to control close
timeout. currently is only used by the http handler, but conceivably could be
passed as a parameter to other subsystems of pilosa/server.Command
since the gossip MemberSet has access to Server, it wasn't really necessary to
pass it a Node object when calling Open on it from Cluster. The end goal is to
have it be removed from Cluster entirely, and have it be Opened externally, and
this is a step toward that.
Exposing Node method on Server doesn't really expose any more than was already
there as the same info can be gotten from LocalStatus with a bit of type
casting. I figured adding the method was a little cleaner, and we could collapse
all the functionality when the dust has settled.
The Cluster.open method has been broken into two parts - one of which happens
earlier (at NewServer time), and the other will eventually just be "waiting to
make sure we've joined the cluster". Right now it's calling Memberset.Open, and
then waiting to make sure the cluster has been joined.
pilosa.Server now implements StatusHandler and EventReceiver and needs only
start a gossip memberset. A gossip member set now takes a server as an argument
explicitly and the maze of handlers and receivers and the starting sequence is
somewhat simplified.
Server now trivially implements EventHandler by passing the call along to its
Cluster object which has the actual implementation. This means that less things
will need to refer to cluster.
cluster.open waits for node to join cluster if it is not the coordinator, and
currently this relies on having the http handler able to receive messages, so
handler needs to be started first.
