'Brings an existing virtual disk under Cinder management.
Detaches the virtual disk identified by existing_ref and attaches
it to a volume backing.
:param volume: Cinder volume to manage
:param existing_ref: Driver-specific information used to identify a
volume'

def manage_existing(self, volume, existing_ref):

    (vm, disk) = self._get_existing(existing_ref)
    create_params = {CREATE_PARAM_DISK_LESS: True}
    backing = self._create_backing(volume, create_params=create_params)
    self.volumeops.detach_disk_from_backing(vm, disk)
    src_dc = self.volumeops.get_dc(vm)
    dest_dc = self.volumeops.get_dc(backing)
    (ds_name, folder_path) = self._get_ds_name_folder_path(backing)
    dest_path = volumeops.VirtualDiskPath(ds_name, folder_path, volume['name'])
    self.volumeops.move_vmdk_file(src_dc, disk.backing.fileName, dest_path.get_descriptor_ds_file_path(), dest_dc_ref=dest_dc)
    profile_id = self._get_storage_profile_id(volume)
    self.volumeops.attach_disk_to_backing(backing, disk.capacityInKB, VMwareVcVmdkDriver._get_disk_type(volume), self._get_adapter_type(volume), profile_id, dest_path.get_descriptor_ds_file_path())
    self.volumeops.update_backing_disk_uuid(backing, volume['id'])
