Comment 3 for bug 1530888

On the sahara side, when changing the tooz backend from memcached to etcd3, instead of failing on _encode_member_id, the code fails on _encode_group_id, which is again probably relevant:

Traceback (most recent call last):
  File "/usr/local/bin/sahara-engine", line 10, in <module>
    sys.exit(main())
  File "/opt/stack/sahara/sahara/cli/sahara_engine.py", line 49, in main
    server.setup_sahara_engine()
  File "/opt/stack/sahara/sahara/main.py", line 109, in setup_sahara_engine
    periodic.setup()
  File "/opt/stack/sahara/sahara/service/periodic.py", line 262, in setup
    pt = _make_periodic_tasks()
  File "/opt/stack/sahara/sahara/service/periodic.py", line 137, in _make_periodic_tasks
    class SaharaPeriodicTasks(periodic_task.PeriodicTasks):
  File "/opt/stack/sahara/sahara/service/periodic.py", line 139, in SaharaPeriodicTasks
    CONF.periodic_coordinator_backend_url, 'sahara-periodic-tasks')
  File "/opt/stack/sahara/sahara/service/coordinator.py", line 99, in __init__
    self.join_group(group_id)
  File "/opt/stack/sahara/sahara/service/coordinator.py", line 69, in join_group
    self.coordinator.join_group(group_id).get()
  File "/usr/local/lib/python3.5/dist-packages/tooz/drivers/etcd3.py", line 218, in join_group
    encoded_group = self._encode_group_id(group_id)
  File "/usr/local/lib/python3.5/dist-packages/tooz/drivers/etcd3.py", line 163, in _encode_group_id
    return self.GROUP_PREFIX + group_id + b"/"
TypeError: can't concat bytes to str