Add 2 new guest: RHEL-5.9 and Fedora-18-beta

RHEL-5.9 is the newest release of RHEL 5 series.
Fedora 18 is the next major release of Fedora series, but it's in beta status now, thus I named it as `Fedora.test`, so that we can keep a development version of Fedora and try some new features on it.