Support N distributed agents

This is the third main feature of this system. The code needs a bunch of
polish, but it actually all works :)

I've tested this briefly with N <= 3.

Currently you have to build your own etcd cluster. It's quite easy, just
run `etcd` and it will be ready. I usually run it in a throw away /tmp/
dir so that I can blow away the stored data easily.

service.go

@@ -51,6 +51,12 @@ func (obj *ServiceType) GetType() string {
 
 // Service watcher
 func (obj *ServiceType) Watch() {
+	if obj.IsWatching() {
+		return
+	}
+	obj.SetWatching(true)
+	defer obj.SetWatching(false)
+
 	// obj.Name: service name
 	//vertex := obj.GetVertex()         // stored with SetVertex
 	if !util.IsRunningSystemd() {