MILWAUKEE'S Rl Hole Saw, Carbide Grit, Black, 4-3/8 In (49-56-0300) https://www.amazon.com/dp/B000CSQMB6/ref=cm_sw_r_cp_api_i_AW5YF9JFNGEK82ZVR7Q0
Use an abrasive hole saw made specifically for plaster ceilings.
http://www.amazon.com/Milwaukee-49-56-0300-Hole-Saw-8-Inch/dp/B000CSQMB6