By Tom Balmforth and Oleksandr Kozhukhar KYIV/LVIV (Reuters) -The European Union was preparing sanctions on Russian oil sales after a major shift on Monday by Germany, Russia’s biggest energy customer, that could deprive Moscow of a large revenue stream within days. The European Commission is expected to propose a sixth package of EU sanctions this week against Russia over its invasion of Ukraine, including a possible embargo on buying Russian oil. Kyiv says that Russia’s energy exports to Europe, so far largely exempt from international sanctions, are funding the Kremlin war effort with milli…