Putting suspend "files" into Ceph RBD images

Currently, Nova "suspend" does a libvirt managed-save, which means that the suspend file (the content of the running guest's RAM) goes to a file in /var/lib/libvirt/qemu/save (a directory which some deployment schemes, like OSA, symlink elsewhere). The libvirt virDomainSave operation, however, can use any file descriptor to save the RAM image to, so in principle there's nothing keeping Nova from opening up a Python rbd file-like object instead and save to that.

This would enable operators to run truly diskless compute nodes, and also create a central point of administration for suspend savefiles.

Related links:
https://libvirt.org/guide/html/Application_Development_Guide-Lifecycle-Save.html