drakx failes to detect USB keys in cooker, because block devices are now named differently in sysfs (using block:<device> naming).

This was fixed for some USB sysfs fields, but the fix wasn't general enough. I've extended it to handle more sysfs fields, such as usb_vendor/id, and to fix our detect_devices::isKeyUsb() function.

USB key are now correctly detected, this should allow the draklive copy wizard to process normally in the next cooker live snapshot.