Create an sdist and return the full file path of the .tar.gz.

def create_sdist(self, tag):
        """Create an sdist and return the full file path of the .tar.gz."""
        logger.info("Making tempdir for %s with tag %s...",
                    self.package, tag)
        self.wrapper.vcs.checkout_from_tag(tag)
        # checkout_from_tag() chdirs to a temp directory that we need to clean up
        # later.
        self.temp_tagdir = os.path.realpath(os.getcwd())
        logger.debug("Tag checkout placed in %s", self.temp_tagdir)
        python = sys.executable
        logger.debug(command("%s setup.py sdist" % python))
        tarball = find_tarball(self.temp_tagdir, self.package, tag)
        return tarball