Correct format string in error message
Due to a syntax error, values are not being interpolated into a
message format string.  This patch corrects the error.
Closes-Bug:
@@ -293,7 +293,7 @@ class SwiftBackupDriver(chunkeddriver.ChunkedBackupDriver):
if etag != md5:
err = _('error writing object to swift, MD5 of object in '
'swift %(etag)s is not the same as MD5 of object sent '
- 'to swift %(md5)s'), {'etag': etag, 'md5': md5}
+ 'to swift %(md5)s') % {'etag': etag, 'md5': md5}
raise exception.InvalidBackup(reason=err)
return md5
