Add RunUntil to the Reflector and Poller to allow early termination

This is useful for test suites where you want to kill your workers
without having to run one test env per execution.

pkg/client/cache/reflector.go

@@ -72,6 +72,12 @@ func (r *Reflector) Run() {
 	go util.Forever(func() { r.listAndWatch() }, r.period)
 }
 
+// RunUntil starts a watch and handles watch events. Will restart the watch if it is closed.
+// RunUntil starts a goroutine and returns immediately. It will exit when stopCh is closed.
+func (r *Reflector) RunUntil(stopCh <-chan struct{}) {
+	go util.Until(func() { r.listAndWatch() }, r.period, stopCh)
+}
+
 func (r *Reflector) listAndWatch() {
 	var resourceVersion string