add line that should have stayed there

docker_dev_start.py

@@ -293,6 +293,7 @@
         logging.debug('Using data volume %s', data_volume_name)
         volume = getVolume(docker_client, data_volume_name)
         # make sure the permission in the volume are correct
+        mount_opts = 'source={},target=/mnt/data'.format(data_volume_name)
         # TODO replace by something cleaner if possible
         call(['docker', 'run', '--rm', '--mount', mount_opts, 'busybox', 'chmod', '777', '/mnt/data'])
         binds.append('{}:/mnt/data'.format(data_volume_name))