By John Davison BAGHDAD (Reuters) – Supporters of Iraqi populist leader Moqtada al-Sadr erected tents and prepared for an open-ended sit-in at Iraq’s parliament on Sunday, in a move that could prolong political deadlock or plunge the country into fresh violence. Thousands of the Shi’ite Muslim cleric’s loyalists stormed into the fortified Green Zone in Baghdad on Saturday, taking over the empty parliament building for a second time in a week as his Shi’ite rivals, most of them close to Iran, try to form a government. “We’re staying until our demands are met. And we have many demands,” a member…