By Vera Eckert, Christoph Steitz and Nina Chestney FRANKFURT/LONDON (Reuters) -German utilities on Thursday said their country needed an early warning system to tackle gas shortages, a day after Russia ordered the switch of contract payments to roubles, raising the risk of a supply squeeze and even higher prices. President Vladimir Putin’s rouble payment demand, which IEA Executive Director Fatih Birol called a “security threat,” added to market nervousness and called into question Russia’s historic claim it is a reliable gas supplier regardless of geopolitics. Putin announced this demand on W…