SmartIO: don't use tmpDir configuration from /etc/sysconfig/rhn/up2date

This change is to make SmartIO use standard system temporary
directories, rather than custom defined tmpDir from up2date config.

Also, this modification means, that spacewalk-backend code (for example
system registration) will not be attempting to open /etc/sysconfig/rhn/up2date,
which wouldn't work for the apache user anyway (0600 file permissions).

On a Fedora 20 system, httpd trying to access /etc/sysconfig/rhn/up2date
would even result into a SELinux denial.