Fail to connect via USB and get logs multiple times

[krichardsson]

From issue bitcraze/crazyflie-lib-python#109

How to reproduce:

1. Start a Roadrunner or Crazyflie
2. Connect via USB to a computer
3. Make sure no Crazradio is connected to the computer
4. Run the https://github.com/bitcraze/crazyflie-lib-python/blob/0.1.7/examples/basiclog.py script.
5. Run the https://github.com/bitcraze/crazyflie-lib-python/blob/0.1.7/examples/basiclog.py script.

Symptoms:

• The script hangs the second time

[AlexisTM]

This is caused by the board to restart due to the watchdog once the USB connection is suspended. Disabling the watchdog shows that the board hangs until the USB connection is reestablished (All LED are frozen until reconnection).

Temporary workaround: Disable the watchdog using the DEBUG flag.

[krichardsson]

Related to #393

[evoggy]

This is closed with the fix for #393.