By Pavel Polityuk and Max Hunder KYIV (Reuters) -Ukraine said on Tuesday that Russia had taken control of most of the eastern industrial city of Sievierodonetsk, a bombed-out wasteland whose capture Moscow has made the principal objective of its invasion. Russia’s all-out assault on the city in Ukraine’s Luhansk province has been met by tough resistance from Ukrainian forces. Russian-backed separatists in Luhansk acknowledged that capturing the city was taking longer than hoped, despite one of the biggest ground attacks of the three-month-long war. After failing to capture the Ukrainian capita…