packaging: setup: io.StringIO needs unicode

I563e8dcfa54e6d23c1e4828c422dcf88ffe1738e fails on fedora19's python.

Related-To: https://bugzilla.redhat.com/1079911
Change-Id: I5622a9fde642330277acf67e56784395daa7d7b8
Signed-off-by: Yedidyah Bar David <didi@redhat.com>