Remove self.__dict__ for formatting strings

Following OpenStack Style Guidelines:
http://docs.openstack.org/developer/hacking/#dictionaries-lists
It is not clear as using explicit dictionaries
and help avoid some errors during refactoring.

Change-Id: Iac53f4ae1fcfa8c0953bf635880f9b883ca9592b

tools/lintstack.py

@@ -187,8 +187,12 @@ class LintOutput(object):
 
     def review_str(self):
         return ("File %(filename)s\nLine %(lineno)d:%(line_content)s\n"
-                "%(code)s: %(message)s" % self.__dict__)
-
+                "%(code)s: %(message)s" %
+                {'filename': self.filename,
+                 'lineno': self.lineno,
+                 'line_content': self.line_content,
+                 'code': self.code,
+                 'message': self.message})
 
 class ErrorKeys(object):