Fix malformed format string.

Also change dict() to {} which is meant to be more efficient:

http://doughellmann.com/2012/11/the-performance-impact-of-using-dict-instead-of-in-cpython-2-7-2.html

This is required for blueprint ec2-error-codes.

Change-Id: Ie32fb43a63ce66c040b5571b13287937bd2df532
Merge "Fix malformed format string."