By Humeyra Pamuk, John Irish and Johan Ahlander BERLIN/STOCKHOLM (Reuters) -NATO and the United States said on Sunday they were confident Turkey would not hold up membership of Finland and Sweden in the Western military alliance, as the two Nordic states took firm steps to join in response to Russia’s invasion of Ukraine. Finnish President Sauli Niinisto confirmed on Sunday that his country would apply to join NATO, while Sweden’s ruling Social Democrats announced an official policy change that would pave the way for their country to apply within days. Swedish Prime Minister Magdalena Andersso…