modify create_guest_user to ensure no duplicate usernames
modify create_guest_user to ensure no duplicate usernames

YaleOutdoors/reservations,YaleOutdoors/reservations,YaleOutdoors/reservations,Amalanag/reservations,YaleSTC/reservations,YaleSTC/reservations,Amalanag/reservations,Amalanag/reservations,YaleSTC/reservations