Make string formatting work on RHEL6 python 2.6

    $ python
    Python 2.6.6 (r266:84292, Nov 21 2013, 10:50:32)
    [GCC 4.4.7 20120313 (Red Hat 4.4.7-4)] on linux2
    Type "help", "copyright", "credits" or "license" for more information.
    >>> "{} {}".format('hello', 'world')
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    ValueError: zero length field name in format
    >>> "{0} {1}".format('hello', 'world')
    'hello world'