If there's one thing we know about Sia, other than the fact that she's an amazing singer/songwriter, it's that she values her privacy. The extent to which she shields her off-stage life came into focus on Tuesday (May 19) when, during an interview with The Morning Mash-Up on SiriusXM she revealed that she adopted two 18-year-old boys to save them from aging out of the foster care system. The 44-year-old singer said, "I actually adopted