rooting check

http://arabiannight.tistory.com/entry/%EC%95%88%EB%93%9C%EB%A1%9C%EC%9D%B4%EB%93%9CAndroid-%EB%A3%A8%ED%8C%85-%EC%97%AC%EB%B6%80-%ED%99%95%EC%9D%B8-%ED%95%98%EA%B8%B0