Bug in apptopo.py in P4D2_2017_Spring

[alex1230608]

Hi,

I think there is a small copy-paste bug at line 57 in P4D2_2017_Spring/utils/mininet/apptopo.py

delay_key = ''.join(sorted([host_name, sw]))

should be

delay_key = ''.join(sorted([sw1, sw2]))

Hope it helps!