Update the cull_idle_servers script

[jtpio]

Update the cull_idle_servers.py script to the latest from JupyterHub: https://github.com/jupyterhub/jupyterhub/blob/8d505548494ad629cc9501f084c6ec4d7646cf98/examples/cull-idle/cull_idle_servers.py

This should fix #547.

• Add / update documentation
• Add tests

[jtpio]

Tested on a VM after setting the timeout to 60s with sudo tljh-config set services.cull.timeout 60.

After starting a named server:

~60 seconds later:

[jtpio]

Some of the changes are coming from the black formatting in jupyterhub.

Also should we add tests for culling named servers? (in this PR or a separate one)
There seems to be some in https://github.com/jupyterhub/the-littlest-jupyterhub/blob/master/integration-tests/test_hub.py

[GeorgianaElena]

Also should we add tests for culling named servers? (in this PR or a separate one)
There seems to be some in https://github.com/jupyterhub/the-littlest-jupyterhub/blob/master/integration-tests/test_hub.py

I believe adding a test would be very useful. Although the PR is pretty big already, I think it's better to have them together (code and test) in this PR to make sure it works before merging. What do you think?

Thanks for working on this @jtpio.

[jtpio]

That would be better indeed.

Taking a closer look, it seems that we would need to add support for named servers to hubtraf too: https://github.com/yuvipanda/hubtraf/blob/37de44df5a2110c18bae4fb426566fddf1c1a05c/hubtraf/user.py#L80

[jtpio]

This will actually be replaced by #559.

[yuvipanda]

@jtpio damn, I did not see this! so sorry :(

[jtpio]

No problem, #559 is much better!

[jtpio]

Fixed by #559.