* Atlantia, ACS strike deal to jointly buy Abertis * Deal values Abertis at more than 18 bln euros * Atlantia to have control over acquisition vehicle * Deal follows Spanish concerns over foreign takeover (Adds details, background) By Francesca Landini and Stefano Bernabei MILAN/ROME, March 14 (Reuters) - Italy's Atlantia and Spanish builder ACS agreed a joint 18 billion euro ($22 billion) bid for Abertis on Wednesday, ending a five-month battle for the Spanish road-tol