Fix the install_dir if "--user" was used.

def _fix_install_dir_for_user_site(self):
        """
        Fix the install_dir if "--user" was used.
        """
        if not self.user or not site.ENABLE_USER_SITE:
            return

        self.create_home_path()
        if self.install_userbase is None:
            msg = "User base directory is not specified"
            raise DistutilsPlatformError(msg)
        self.install_base = self.install_platbase = self.install_userbase
        scheme_name = os.name.replace('posix', 'unix') + '_user'
        self.select_scheme(scheme_name)