By Michael Shields VIENNA (Reuters) - Call it the battle for grandma's passbook. That is how politicians here are framing a debate over whether Austria should roll back banking secrecy and share information on depositors with European partners and the United States. Luxembourg's decision this week to open its books has fixed attention on Austria, the last EU holdout. The discussion has touched a nerve in a country where the confidentiality banks offer is so cherished that banking secrecy is anchored in the constitution. ...