Notify watchers when the store is closed

[alexbrand]

In it's current implementation, the store does not let existing watchers know that the store is getting closed. Also, there is nothing preventing a client that has a handle on the store to create new watches after the store has been closed.

We need to look into possible solutions here. This might have an impact on the watch API.

[alexbrand]

Once this is fixed, the goroutine leak tests that exist in pkg/controller should be enabled.