It is not an uncommon scene: a waiting room filled with patients hoping to see a doctor. But the crowd of up to 100 people that gathered each day outside the Astramed clinic at 1228 Southern Boulevard in the Bronx, clamoring to get a prescription for the painkiller oxycodone, was a different story, the authorities say. The clinic was controlled by drug traffickers, and the patients, doctors, prescriptions — and even urine samples — were part of a vast and elaborate scheme to divert oxycodone for sale on the street, the authorities said on Wednesday.