* Pre-Greek vote preparations by central banks reassure * U.S. economic data comes in weaker than expected * Dow up 0.9 pct, S&P 500 up 1 pct, Nasdaq up 1.3 pct By Rodrigo Campos NEW YORK, June 15 (Reuters) - U.S. stocks rallied on Friday to close a second straight week of gains on hopes of collective action from global central banks if Sunday's election in Greece triggers market turmoil. The news helped offset the latest round of weak U.S.