Hardcoded serial port device node

[satoshinm]

Attempting to use pirate-swd on my system, but it fails to open the device:

pirate-swd $ python flashSTM32.py  
Traceback (most recent call last):
  File "flashSTM32.py", line 41, in <module>
    main()
  File "flashSTM32.py", line 18, in main
    busPirate = PirateSWD("/dev/ttyUSB0")
  File "pirate-swd/PirateSWD.py", line 7, in __init__
    self.port = serial.Serial(port = f, baudrate = 115200, timeout = 0.01)
  File "/Library/Python/2.7/site-packages/serial/serialutil.py", line 240, in __init__
    self.open()
  File "/Library/Python/2.7/site-packages/serial/serialposix.py", line 268, in open
    raise SerialException(msg.errno, "could not open port {}: {}".format(self._port, msg))
serial.serialutil.SerialException: [Errno 2] could not open port /dev/ttyUSB0: [Errno 2] No such file or directory: '/dev/ttyUSB0'

since it has a different name (/dev/tty.usbserial in my case). Suggestion: add a command-line option to specify an alternate serial port (--port /dev/tty.usbserial). I might help with this later... for now I changed it locally hardcoded to my device.