'Retrieve data by key from the persistent store on the backend.
Example response: {"key": "cinder-snapshots", "value": "[]"}
:param key: the persistent store to retrieve
:returns: a json body representing the value of the store,
or an empty json object'

def list_backend_store(self, key):

    path = self.RESOURCE_PATHS.get('persistent-store')
    try:
        resp = self._invoke('GET', path, **{'key': key})
    except exception.NetAppDriverException:
        return dict()
    else:
        data = resp['value']
        if data:
            return json.loads(data)
        return dict()
