'Helper function to check if snapVx sync session is complete.
:param array: the array serial number
:param source_device_id: source device id
:param snap_name: the snapshot name
:param target_device_id: the target device id
:returns: defined -- bool'

def _is_sync_complete(self, array, source_device_id, snap_name, target_device_id):

    defined = True
    session = self.get_sync_session(array, source_device_id, snap_name, target_device_id)
    if session:
        defined = session['defined']
    return defined
