By Lili Bayer and Andrew Gray ANKARA, July 8 (Reuters) - NATO’s Europeanleadersaimto convince Donald Trumpon Wednesdaytore-committothemilitaryallianceat a summit in Ankaraafterthe U.S. president revived his disputes with them over the Iran warand Greenland. Following his arrival in the Turkish capital on Tuesday, Trump said he might have boycotted the summit had it not been for his friendship with the host, President Tayyip Erdogan, and he did not rule out further troop withdrawals from Europe.