This error may occur when busnum is incorrect:
"IOError: [Errno 16] Device or resource busy"
Refer to this Adafruit Forum issue for more information
"LED Backpack not working on beaglebone black with debian"
https://forums.adafruit.com/viewtopic.php?f=49&t=140344
Signed-off-by: Drew Fustini <drew@pdp7.com>