Glastonbury organiser Emily Eavis defended the festival's line-up amid criticism of there being a lack of rock bands as pop star Dua Lipa prepares to headline Friday's music.The main stages open at Worthy Farm on Friday as this sees headline performances from Dua Lipa, British rock band Coldplay and American soul singer SZA, while Canadian country star Shania Twain will play the coveted Legends slot.