OpenNebula

As reported by Joel Merrick on IRC:

The attach-disk mechanism requires additional handling inside the generated to take account of the extra node info in the XML
i.e. no need for auth or secrets if it's file based etc..

1) ensure clone/snaphot of datablock (this creates a one-IMAGEID-VMID-SNAPID format)
2) create conditionals to handle the different XML schema for rbd vs. file
3) pull extra variables from XML/XPATH
4) form correct XML to allow the attach_disk script to work

Current:

<disk type='network' device='disk'>
  <driver name='qemu' type='raw' cache='writeback'/>
  <source protocol='rbd' name='ssd/one-97'/>
  <target dev='vdb'/>
</disk>

Should be:

    <disk type='network' device='disk'>
            <source protocol='rbd' name='ssd/one-95-2620-0'>
                <host name='xxx' port='6789'/>
                <host name='xxx' port='6789'/>
                <host name='XXX' port='6789'/>
            </source>
            <auth username='libvirt'>
                <secret type='ceph' uuid='NO-THANKS'/>
            </auth>
            <target dev='vda'/>
            <driver name='qemu' type='raw' cache='writeback'/>
        </disk>