sets or changes a bucket's acl to a predefined (canned) value. 
           We include a version_id argument to support a polymorphic 
           interface for callers, however, version_id is not relevant for 
           Google Cloud Storage buckets and is therefore ignored here.

def set_canned_acl(self, acl_str, key_name='', headers=None, 
                       version_id=None):
        """sets or changes a bucket's acl to a predefined (canned) value. 
           We include a version_id argument to support a polymorphic 
           interface for callers, however, version_id is not relevant for 
           Google Cloud Storage buckets and is therefore ignored here.""" 
        return self.set_canned_acl_helper(acl_str, key_name, headers, 
                                          STANDARD_ACL)