[Libvir] support for hvm guests

Daniel, FYI, I'm working on a patch to support hvm guests. Attached is the work thus far. Calling "virsh dumpxml some_hvm_guest" will (almost) correctly dump xml config info on hvm guests. Needs to handle "type=ioemu" component of VIF specification. Currently in the XML there is a type attribute for the interface element that specifies bridge, route, etc. How would you like to structure the interface element and its children to account for hvm guests? Using "virsh create file" where file contains XML config for hvm guests may be close to working but I haven't tested it yet. There are several options that need to be added to the XML to support hvm guests. If we can agree on the structure I can add the functionality. Regards, Jim