Grab accelerator set off the end of the list instead of by index

[adamnovak]

We were using a magic [3] to get the accelerator set, and then I added a new resource pool in #4461 and didn't manually test GPU support.

This now uses a slightly less magic [-1] and should keep working as long as accelerators are the last resource type.

This will fix #4503.

Changelog Entry

To be copied to the draft changelog by merger:

• Single machine batch system now works with GPUs again

Reviewer Checklist

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    contrib/admin/test-pr otheruser theirbranchname issues/XXXX-fix-the-thing
    

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• Read through the code changes. Make sure that it doesn't have:
  • Addition of trailing whitespace.
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Merger Checklist

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[adamnovak]

I should manually test this to make sure it actually solves the problem.

[adamnovak]

OK I manually tested this and it does in fact work great.

@DailyDreaming I'm going to merge this without waiting for a review, since it's just a couple characters and it fixes a user issue.

My test:

cat >gpu_test.wdl <<'EOF'
version 1.0
workflow GPUTest {
    input {
    }
    call testGPU {
    }
    output {
        File result = testGPU.result
    }
}

task testGPU {
    input {
    }
    command <<<
        nvidia-smi
    >>>
    output {
        File result = stdout()
    }
    runtime {
        memory: "1 GB" 
        cpu: 1
        gpuType: "nvidia-tesla-t4"
        gpuCount: 1
        disks: "local-disk 1 SSD"
    }
}
EOF

echo "{}" >empty.json

toil-wdl-runner --logDebug --retryCount=0 gpu_test.wdl empty.json -o test-out