Remove unnecessary string conversion

Using str(obj) will fail if the object is a unicode string and contains extended characters. However, since the argument to the % operator is certainly a tuple, there is no question as to the fact that the passed object is to be converted to a string (ascii OR unicode).

To clarify:

This will NOT always work:
```print("%s" % notastring)```
such as when notastring is a tuple.

These will work:
```print("%s" % (notastring,))
print("%s %s" % (notastring, somethingelse))```

This is likely not the only place where str() will need to be removed because of the possibility of a unicode string.

This was discovered when F19 used extended characters in the release name. Anywhere a string containing the os_version is passed to str(), this problem will present itself.