Adds a device to the list of devices we know about.

def add_device(dev):
    """Adds a device to the list of devices we know about."""
    global DEV_IDX, DEFAULT_DEV
    with DEV_LOCK:
        for idx in range(len(DEVS)):
            test_dev = DEVS[idx]
            if test_dev.dev_name_short == dev.dev_name_short:
                # This device is already in our list. Delete the old one
                if test_dev is DEFAULT_DEV:
                    DEFAULT_DEV = None
                del DEVS[idx]
                break
        if find_device_by_name(dev.name):
            # This name is taken - make it unique
            dev.name += '-%d' % DEV_IDX
        dev.name_path = '/' + dev.name + '/'
        DEVS.append(dev)
        DEV_IDX += 1
        if DEFAULT_DEV is None:
            DEFAULT_DEV = dev