The “unknown item” that forced a brief evacuation of the White House Sunday night and drew a Hazmat team from Washington, DC, Fire and EMS to the executive mansion initially tested positive for cocaine, according to a dispatch call made that evening. “We have a yellow bar stating cocaine hydrochloride,” a DC firefighter stated in a radio communication at 8:49 p.m. on Sunday. “Bag it up and take it out,” the firefighter told the Hazmat team. The white powdery substance was found in the residence’s library, according to the dispatch call. The Secret Service told The Post the agency “does not comment on an active ... (full story)