With 2 headliners confirmed for Gastonbury 2017, NME columnist speculates on who could be the last headliner for this year’s lineup.     Confirmed Headliners: Radiohead, Foo Fighters Rumours: Guns N' Roses -  odds 12/1 Kasabian - odds 6/4 The Stone Roses - odds 4/1 Ed Sheeran - odds 4/1 Rihanna - odds 6/1 Daft Punk - odds 9/1 Gorillaz - odds 9/1 Lady Gaga - odds 16/1 Why she’d be great:  She’s stepping in for Beyonce at Coachella, so