LOS ANGELES (Reuters) - Scottish DJ Calvin Harris may not be the most recognizable face in the U.S. music scene, but after writing Rihanna's biggest chart hit and with two other top 20 singles, Harris is fast becoming a chart staple. Harris, 28, found success in the UK over the last five years before storming the Billboard Hot 100 earlier this year with "We Found Love," a dance-infused dark love song featuring Rihanna's vocals that became one of 2012's biggest hits. ...