[Libvirt-cim] [PATCH 0 of 2] VCPU xml generation

We have, so far, been ignoring the vcpu bit of XML generation, mostly because we treat multiple vcpus as separate devices in the CIM world, but as a single integral value in the libvirt world. This set changes the way the xml generation code is structured to handle batches of devices, and then adds support for generating the VCPU node. It's a little strange, but I decided that allowing a given device class to modify and append the XML being generated for its class was the safest way to handle all the cases without separating things out too much. Comments on this approach are welcomed. I believe that this set will also make ModifyResource in VSMS work for VCPUs as well, since it should be able to generate updated XML with the new vcpu count after such an operation. More testing to determine if additional work will be required needs to be done.