By Marwa Rashad LONDON (Reuters) -Europe vowed to stay united against Russia’s demand that they pay for its gas in roubles, as the threat of an imminent supply halt eased on Friday. European capitals have been bracing for a disruption to gas imports as Russian President Vladimir Putin seeks retaliation over Western sanctions for the Feb. 24 invasion of Ukraine. Some buyers and governments were working on ways to potentially pay for gas in roubles as Moscow in recent days has raised the spectre of cutting gas supply if its payment terms are not met. With weeks left before bills are due, governm…