[libvirt] virt-install feature request

So virt-install is a really nice piece of software, but it's a bit too complicated for our use case :). We would want some mode of it to simply generate XML and go home :). The use case is that we have a script which carries out a number of other actions in addition to creating a guest, and creating a guest and putting an OS on it are two separate steps. It would also be nice to have some command line interface to modify a guest's boot selection, for example, changing from PXE to local disk. Even nicer would be a concept of boot order - we have a setup where the first normal boot order is PXE, and if that fails (which it should a majority of the time) then go to local disk.