* GDP grew 2.1 pct on year in Q2 (Reuters poll 2.65 pct)* Finance minister sees threat to 4 pct 2014 target* Lira at weakest since late March* Slower growth will heighten pressure for rate cuts(Adds Economy Minister Nihat Zeybekci)By Ayla Jean Yackley and Behiye Selin TanerISTANBUL, Sept 10 (Reuters) - Turkey&aposs economy grew less than expected in the second quarter, increasing political pressur