Fix Z-Order Bug SpriteBatchNode

Fixes Z-ORder bug for SpriteBatchNode. Previously, setting the zOrder on childs of SpriteBatchNode would not reorder the children. The reason is that Node::setLocalZOrder would set _localZOrder = z before the parent would check zOrder == child->getLocalZOrder() causing the reorderChild methods to return without reordering the children.

Please refer to https://github.com/cocos2d/cocos2d-swift/issues/598 for additional information.