CacheConfig does not extend MutableConfiguration anymore

cache.getConfiguration now returns an immutable instance, as stated in the spec
listenerConfigurations should be thread-safe now
added null check for waiting count-down completion of sync listeners
I don't know actually, it was @asimarslan 's fix and I just copy/pasted it.
he was mentioning about that this could be happen only if the listener de-registered before counting down. so he was stating that only a null check should be fine.