If no kinect is attached use the usb to serial converter's id instead

In case their is no kinect attached to the turtlebot (maybe their
is an Asus Xtion instead, sadly those don't appear to have serial #s)
attempt to build an id from the usb to serial converter that is
connected to /dev/ttyUSB0 in the hopes that this can uniquely identify
the turtlebot.