[libvirt] [PATCH V3] Add libxenlight driver

Hi All, Another update to the libxenlight driver for Xen 4.1. The primary change in this version is reservation of vnc ports within the driver when autoport=yes. libxenlight does not provide a mechanism to retrieve the auto-selected port and the 'vncunused' option is not in upstream qemu anyhow, so best to avoid it. I've tested the following operations on both pv and hvm linux guests: define, undefine, start, create, shutdown, reboot, destroy, getinfo, and dumpxml. I've also done some minimal testing with virt-manager, e.g. starting a previously defined domain and connecting to its graphical console. Thanks for your review and comments. Regards, Jim