Improve CUDAWorker scheduler-address parsing and __init__

[necaris]

Allows scheduler argument to be optional, and uses dask.config to check the scheduler-address rather than dictionary lookup (this allows e.g. environment variables like DASK_SCHEDULER_ADDRESS to be correctly parsed)

[GPUtester]

Can one of the admins verify this patch?

[GPUtester]

Can one of the admins verify this patch?

[GPUtester]

Can one of the admins verify this patch?

[jrbourbeau]

For context, setting the DASK_SCHEDULER_ADDRESS environment variable puts scheduler_address (note the underscore) into Dask's config system. We generally try to use dask.config.get when interacting with config values as it treats underscores and hyphens the same (xref dask/distributed#2676)

The scheduler=None change is so CUDAWorker can better handle other ways in which the scheduler address can be specified (e.g. scheduler_file or scheduler-address configuration option). There's additional logic here

dask-cuda/dask_cuda/cuda_worker.py

Lines 130 to 134 in 3811951

	if not scheduler and not scheduler_file and "scheduler-address" not in config:
	raise ValueError(
	"Need to provide scheduler address like\n"
	"dask-worker SCHEDULER_ADDRESS:8786"
	)

that will still catch cases when no scheduler address is specified

[quasiben]

ok to test

[quasiben]

Thank you @necaris and the comment @jrbourbeau !

[quasiben]

@necaris i made this change on your behalf -- hope you don't mind

[quasiben]

Thanks again @necaris

[necaris]

@quasiben very welcome!

[codecov-commenter]

Codecov Report

Merging #397 into branch-0.16 will increase coverage by 0.05%.
The diff coverage is 100.00%.

@@               Coverage Diff               @@
##           branch-0.16     #397      +/-   ##
===============================================
+ Coverage        60.07%   60.13%   +0.05%     
===============================================
  Files               17       17              
  Lines             1345     1342       -3     
===============================================
- Hits               808      807       -1     
+ Misses             537      535       -2     

Impacted Files	Coverage Δ
dask_cuda/cuda_worker.py	72.28% <100.00%> (+0.52%)	⬆️
dask_cuda/local_cuda_cluster.py	82.95% <100.00%> (+0.93%)	⬆️

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