Make obstacle appearance a bit more nuanced

[chrisgrounds]

while True:
# ...
    player.move()                                                                                                                             
    floor.draw()                                                                                                                              
    obstacle.draw()   

The method draw on the obstacle object is called every game loop.

Want to add some logic that makes it get called only (a) randomly or (b) when a certain condition is met (timer?)