Fix ClusterManager.dashboard_link

[stuarteberg]

Fixes #288

Specifically, fixes this error in the dashboard_link attribute of ClusterManager:

  File "/miniconda/envs/myenv/lib/python3.7/site-packages/dask_jobqueue/deploy/cluster_manager.py", line 146, in dashboard_link
    port = self.scheduler.services["bokeh"].port
KeyError: 'bokeh'

[lesteve]

I think it's fine to do bokeh -> dashboard without backward compatibility as I said in #288 (comment).

Would it be possible and not too hard to add a test for this? Currently our tests are passing with distributed >= 2, e.g. https://travis-ci.org/dask/dask-jobqueue/jobs/560794336.

[stuarteberg]

Would it be possible and not too hard to add a test for this?

Ok, done!

[lesteve]

Thanks a lot for the additional test!

format_dashboard_link has been added in distributed 2.1 in this commit dask/distributed@bf65f7a. I am in favour of requiring
distributed >= 2.1 (simpler). Note that 2.0 and 2.1 were released two weeks apart (25 June and 8 July): https://distributed.dask.org/en/latest/changelog.html#id1

@guillaumeeb any strong objections on this one?

[guillaumeeb]

I'm perfectly fine with this.

Note that you've got more than all my trust, and you're very welcome to take this kind of decision without me as a core maintainer, especially during summer holydays!

[lesteve]

Thanks for your feedback, it's always good to have a second opinion on this kind of decisions!

Let's merge this one then!

[lesteve]

Thanks a lot for the PR @stuarteberg!