Solve the notification on startup pod status notification race condition

This solves the race condition as described in
https://github.com/virtual-kubelet/virtual-kubelet/issues/836.

It does this by checking two conditions when the possible race condition
is detected.

If we receive a pod notification from the provider, and it is not
in our known pods list:
1. Is our cache in-sync?
2. Is it known to our pod lister?

The first case can happen because of the order we start the
provider and sync our caches. The second case can happen because
even if the cache returns synced, it does not mean all of the call
backs on the informer have quiesced.

This slightly changes the behaviour of notifyPods to that it
can block (especially at startup). We can solve this later
by using something like a fair (ticket?) lock.

node/pod_test.go

@@ -53,6 +53,7 @@ func newTestController() *TestController {
 			done:            make(chan struct{}),
 			ready:           make(chan struct{}),
 			podsInformer:    iFactory.Core().V1().Pods(),
+			podsLister:      iFactory.Core().V1().Pods().Lister(),
 		},
 		mock:   p,
 		client: fk8s,