Check cache is synced first before sleeping

If a cache was already synced, cache.WaitForCacheSync would
always take 100ms to complete because the PollUntil method will
sleep first before checking the condition.  Switching to
PollImmediateUntil will ensure already synced caches will return
immediately.  For code that has, for example, 20 informers, the time
to check the cache was in sync would take at least 2 seconds, but with
this change it can be as fast as you can actually load the data.

Signed-off-by: Darren Shepherd <darren@rancher.com>

Kubernetes-commit: 8a58f332dd62b68ae22c67585002defe6aeb4b04

tools/cache/shared_informer.go

@@ -209,7 +209,7 @@ func WaitForNamedCacheSync(controllerName string, stopCh <-chan struct{}, cacheS
 // if the controller should shutdown
 // callers should prefer WaitForNamedCacheSync()
 func WaitForCacheSync(stopCh <-chan struct{}, cacheSyncs ...InformerSynced) bool {
-	err := wait.PollUntil(syncedPollPeriod,
+	err := wait.PollImmediateUntil(syncedPollPeriod,
 		func() (bool, error) {
 			for _, syncFunc := range cacheSyncs {
 				if !syncFunc() {