By Piya Sinha-Roy LOS ANGELES (Reuters) - Singer Beyonce will kick off the first BET three-day music festival on Friday, ahead of the BET awards this weekend, as the network hopes to attract more fans to music and comedy by black artists. The annual BET awards, now in its 13th year, celebrate black musicians, actors and athletes across a variety of categories spanning music, film and sport. It is televised on the cable TV network BET, Black Entertainment Television, part of Viacom Inc. ...