[Libvirt-cim] [PATCH 0 of 2] Add VirtualSystemSnapshotService

This adds basic support for the VirtualSystemSnapshotService. Since the service seems to assume that a system can be snapshotted while running (which Xen cannot do), we provide a terminal snapshot and fake a running snapshot by doing a save/resume. Still to be done is adding the Capabilities support, as well as making the VSSD provider expose an additional VSSD for the snapshot, as required by the SVP.