Collect at every scrape, rather than at regular intervals.

Switch to Update using the Collecter Collect interface, due to not knowing all
metricnames in all modules beforehand we can't use Describe and thus the full
Collecter interface.

Remove 'updates', it's meaning varies by module and doesn't add much.

collector/time.go

@@ -32,16 +32,13 @@ func NewTimeCollector(config Config) (Collector, error) {
 		config: config,
 	}
 
-	if _, err := prometheus.RegisterOrGet(systemTime); err != nil {
-		return nil, err
-	}
 	return &c, nil
 }
 
-func (c *timeCollector) Update() (updates int, err error) {
-	updates++
+func (c *timeCollector) Update(ch chan<- prometheus.Metric) (err error) {
 	now := time.Now()
 	glog.V(1).Infof("Set time: %f", now.Unix())
 	systemTime.Set(float64(now.Unix()))
-	return updates, err
+	systemTime.Collect(ch)
+	return err
 }