nutdrv_qx: improve support for '(ACK/(NAK' and Voltronic Power P98 UPSes …

In 'mecer' subdriver's claim function try to get protocol (QPI, for Voltronic Power devices) used by the UPS:
- supported devices are Voltronic Power's P98 units
- if the UPS doesn't support the QPI command, use its reply to identify whether it uses '(ACK\r'/'(NAK\r' replies

This way we can catch '(ACK/(NAK' devices, while previously the 'mecer' subdriver was 'hidden' by the 'megatec' (echo back/'ACK/NAK') one.
Plus Q1 units with 'ACK'/'NAK' replies or echoing back not supported and rejected commands are no longer wrongly 'claimed' by the 'mecer' subdriver.