Replace legacy commands with 'dask worker' and 'dask scheduler'.

[wilson]

Hi there.
I'm not 100% the change I made re: GPU workers is correct.
I believe it to be, but I haven't used it in anger.
Looking at the dask-cuda project, it does look like dask-cuda-worker is deprecated just like dask-worker.

Anyway, this PR fixes a pair of warnings:

distributed/cli/dask_scheduler.py:140: FutureWarning: dask-scheduler is deprecated and will be removed in a future release; use `dask scheduler` 
distributed/cli/dask_worker.py:264: FutureWarning: dask-worker is deprecated and will be removed in a future release; use `dask worker` instead

In doing this, I realized that the worker_command option is not used anywhere, so this PR also removes the remaining references to it.

[jacobtomlinson]

This look great thanks.

In dask-cuda we replaced dask-cuda-worker with dask cuda worker. That's all that should be changed. Sorry you went down the resources path, that's not needed.

[wilson]

This look great thanks.

In dask-cuda we replaced dask-cuda-worker with dask cuda worker. That's all that should be changed. Sorry you went down the resources path, that's not needed.

Oh, gotcha; I'll change it up.

[wilson]

OK, rebased off main and all looks green.

[jacobtomlinson]

Thanks. Couple of questions.

[jacobtomlinson]

I'm apprehensive about having a None in this string. Have you tested that this works as expected?

[wilson]

There's a None but it gets filtered out before we use it.

[jacobtomlinson]

I found the introduction and filtering of None hard to parse when reviewing this.

I think it would be more readable to have something like

if self._gpu:
    _command = ["dask", "cuda", "worker"]
else:
    _command = ["dask", "worker"]
_command += [OTHERARGS...]

[jacobtomlinson]

I'm curious why create this variable?

[jacobtomlinson]

Same here

[wilson]

To both the above, just so it was more visible that we're filtering Nones out.
That seemed like the easiest way to have a variable number of arguments in the command.

[jacobtomlinson]

There's been no activity here for a while so I'm going to close this PR out. @wilson if you have the desire to pick this up I'd happily give it another review.