For at least the fourth time recently, brazen armed robbers have strong-armed a Downtown Jersey City parking lot attendant into handing over the keys to multiple high-end vehicles early Thursday morning, Jersey City police confirmed. Two Porsches and a Maserati were stolen at gunpoint from a parking garage at 2 Second St. on the waterfront by four men, all armed, at 12:30 a.m., police said in radio transmissions. Jersey City spokesman Stan Eason confirmed that it was the second time that lot had been victimized. Last month a parking lot on Christopher Columbus Drive, also Downtown, was twice r…