'Ensure concerto snapshot policy exists on cinder volume.
A snapshot policy is required by concerto in order to create snapshots.
:param volume_id:  Cinder volume ID corresponding to the backend LUN
:raises:
VolumeBackendAPIException: when snapshot policy cannot be created.'

def _ensure_snapshot_policy(self, volume_id):

    if (not self.vmem_mg.snapshot.lun_has_a_snapshot_policy(lun=volume_id)):
        res = self.vmem_mg.snapshot.create_snapshot_policy(lun=volume_id, max_snapshots=CONCERTO_DEFAULT_POLICY_MAX_SNAPSHOTS, enable_replication=False, enable_snapshot_schedule=False, enable_cdp=False, retention_mode=CONCERTO_DEFAULT_POLICY_RETENTION_MODE)
        if (not res['success']):
            msg = (_('Failed    to    create    snapshot    policy    on    volume    %(vol)s:    %(res)s.') % {'vol': volume_id, 'res': res['msg']})
            raise exception.VolumeBackendAPIException(data=msg)
