COMPUTE_STORAGE_VIRTIO_FS allows us to report this trait and use
it to filter hosts that support virtio filesystems.
COMPUTE_MEM_BACKING_FILE allows us to report this trait and use
it to filter hosts that supports file-backed memory.
These both traits are necessary to support sharing files with
virtiofs and so forth with manila shares.
Implements: blueprint libvirt-virtiofs-attach-manila-shares
Change-Id: I89419cf1649f48106d84cc84e688df7a065f470a
a097c3f7b0