MADRID (Reuters) – Spain-based cabin crew at Ryanair plan to strike for 12 days this month to demand better working conditions, the USO and SICTPLA unions said on Saturday, raising the prospect of travel chaos as the summer tourist season gets under way. The announcement came on the final day of the crews’ current strike, which began on Thursday and forced Ryanair to cancel 10 flights in Spain on Saturday. Cabin crew will strike on July 12-15, 18-21 and 25-28 across the 10 Spanish airports where Ryanair operates, the unions said in a statement. “The unions and crew of Ryanair … demand a chan…