'Manage an existing lun in the array.
The lun should be in a manageable pool backend, otherwise
error would return.
Rename the backend storage object so that it matches the,
volume[\'name\'] which is how drivers traditionally map between a
cinder volume and the associated backend storage object.
.. code-block:: python
manage_existing_ref:{
\'source-id\':<lun id in VNX>
or
.. code-block:: python
manage_existing_ref:{
\'source-name\':<lun name in VNX>'

def manage_existing(self, volume, existing_ref):

    return self.adapter.manage_existing(volume, existing_ref)
