RemoteCache failure if RemoteCacheManager not started

If the RemoteCacheManager is not started then an misleading exception is being thrown back to the user whenever trying to invoke a method on the remote cache: "org.infinispan.client.hotrod.exceptions.HotRodClientException: Could not instantiate class: null". This should be replaced with a proper exception being replaced, stating to the user that RemoteCacheManager needs to be started before using the cache.