Re: [libvirt] Improve heuristic for default guest architecture

In libvirt 0.6.1, if you create a domain description of type 'kvm' without an arch set on an x86-64 host, you would get an i686 qemu guest rather than the expected x86-64 kvm guest. This is because virCapabilitiesDefaultGuestArch doesn't take the domain type into consideration, so it just returned the first hvm architecutre that has been registered, which is i686. After applying Dan P's patch, http://www.redhat.com/archives/libvir-list/2009-March/msg00281.html, I now get a i686 kvm guest, since kvm now can do i686 guests from libvirt. This is certainly an improvement, but I think a more reasonable default is to attempt to match the host's architecture. This patch makes virCapabilitiesDefaultGuestArch also check the domain type, and also gives preference to a guest architecture that matches the host's architecture.