'Manages an existing image.
Renames the image name to match the expected name for the volume.
Error checking done by manage_existing_get_size is not repeated.
:param volume:
volume ref info to be set
:param existing_ref:
existing_ref is a dictionary of the form:
{\'source-name\': <name of rbd image>}'

def manage_existing(self, volume, existing_ref):

    with RADOSClient(self) as client:
        rbd_name = existing_ref['source-name']
        self.RBDProxy().rename(client.ioctx, utils.convert_str(rbd_name), utils.convert_str(volume.name))
