At long last it's happened: Someone has upgraded SolarCity (NASDAQ: SCTY) stock -- and not despite Tesla Motors' (NASDAQ: TSLA) questionable decision to bid to buy it, but because of it.Yesterday, at the same time as analysts at Argus were announcing yet another downgrade of Tesla stock and calling the bid "ill-timed," risky for Tesla stock holders, and "inappropriate," analysts at Avondale Partners were looking closely at the other side of the equation.