Python 2.6 compatibility

[kedare]

When running on Python 2.6, I get the same issue that what we can find here :

https://github.com/etianen/django-watson/issues/4

The code is using {}, that is only supported since Python 2.7

Traceback (most recent call last):
  File "/opt/rpm-s3/bin/rpm-s3", line 261, in <module>
    main(options, args)
  File "/opt/rpm-s3/bin/rpm-s3", line 246, in main
    update_repodata(options.repopath, args, options)
  File "/opt/rpm-s3/bin/rpm-s3", line 163, in update_repodata
    s3grabber = S3Grabber(s3base, options.visibility, options.region)
  File "/opt/rpm-s3/bin/rpm-s3", line 46, in __init__
    self.bucket = getclient(base, region)
  File "/opt/rpm-s3/bin/rpm-s3", line 118, in getclient
    host="s3-{}.amazonaws.com".format(region)
ValueError: zero length field name in format