By Pavel Polityuk and Tom Balmforth KYIV (Reuters) -Ukraine restored power on Thursday to two of its four nuclear power plants but much of the country remained consigned to freezing darkness by the most devastating Russian air strikes on its energy infrastructure so far. Viewed from space, Ukraine has become a dark patch on the globe at night, satellite images released by NASA showed, following repeated barrages of Russian missiles in recent weeks. With temperatures falling below zero, authorities were working to get the lights and heat back on. Russia’s latest missile barrage killed 10 people…