Origin/hpc xen

Committing all the code that works with OpenStack PCI Passthrough. This is based on the the boris-42 codeset 5 from grizzly master. Also includes a few minor changes to make Xen work with libvirt. However for pci-passthrough to work, still need custom libvirt 0.10.2.6-1 compiled RPMs.  Tested working on HP6 machine with Xen 4.2.2-22.el6 from Centos6 xen repository. To use Raw or QCOW2 image, make sure to update the image vm_mode=hvm in glance after initial upload.   For more information on generic pci passthrough support in OpenStack, please visit here: https://blueprints.launchpad.net/nova/+spec/pci-passthrough-base