OnEnterTransitionDidFinish was called twice when a node is added in onEnter

Fix ported from cocos2d-iphone:
https://github.com/cocos2d/cocos2d-iphone/commit/99b7bef8800bd850f6b0c7dc1eb09d8e81fd80f7
Merge pull request #2650 from varlucian/onentertransitionfinnished

OnEnterTransitionDidFinish was called twice when a node is added in onEnter