By Polina Nikolskaya DONETSK, Ukraine (Reuters) -Russia’s President Vladimir Putin was set to oversee exercises by strategic nuclear missile forces on Saturday as Western leaders gathered in Munich, fearful that he could order troops massed on Ukraine’s border to invade at any time. Russian-backed separatist leaders in eastern Ukraine declared a full military mobilisation, a day after ordering women and children to evacuate to Russia, citing the threat of an imminent attack by Ukrainian forces. Kyiv flatly denied the accusation and Washington said it was part of Russia’s plan to create a prete…