BRUSSELS — European airports face a looming shortage of jet fuel as the ripple effect of Iran’s closure of the Strait of Hormuz to most oil shipments hits the continent. London Heathrow and other U.K. airports are the most vulnerable, with fuel-caused flight cancellations already underway . Regional airline Skybus has ended one route due to fuel prices. French airports could be next, according to estimates by energy analysis firm Kpler. “France has the next-biggest deficit between supply and