usb_test.c implements a USB serial (CDC) interface.  After flashing the
Ubertooth board, unplug the board from USB and plug it in again.  A new USB
device should be detected.  For example (on Linux):

# dmesg

[134437.193956] usb 8-1.2: New USB device found, idVendor=ffff, idProduct=0005
[134437.193962] usb 8-1.2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[134437.193969] usb 8-1.2: Product: Ubertooth serial
[134437.193974] usb 8-1.2: Manufacturer: http://ubertooth.sourceforge.net/
[134437.193980] usb 8-1.2: SerialNumber: 00000001

The USBLED should be illuminated at this point.

Further testing of the USB serial interface can be done by attaching a USB
serial driver to the device.  On Linux, you can do this by disconnecting the
Ubertooth board (and any other USB serial devices) and then:

# modprobe -r usbserial
# modprobe usbserial vendor=0xffff product=0x0005

Then connect the Ubertooth board.  You should now have a new USB serial port:

# dmesg

[135221.849162] usbserial_generic 8-1.2:1.1: generic converter detected
[135221.849391] usb 8-1.2: generic converter now attached to ttyUSB1

You can connect to this port (for example with minicom) and type some
characters.  Each character should echo back to the screen, and USRLED should
toggle on or off with each character typed.
