fixes for dask

[djarecka]

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Summary

Checklist

• [ ] I have added tests to cover my changes (if necessary)
• [ ] I have updated documentation (if necessary)

[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and project coverage change: -4.10% :warning:

Comparison is base (29d3d1f) 82.88% compared to head (c7384b9) 78.79%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #689 +/- ## ========================================== - Coverage 82.88% 78.79% -4.10% ========================================== Files 22 22 Lines 4845 4848 +3 Branches 1391 1392 +1 ========================================== - Hits 4016 3820 -196 + Misses 825 823 -2 - Partials 4 205 +201 ``` | [Flag](https://app.codecov.io/gh/nipype/pydra/pull/689/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipype) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/nipype/pydra/pull/689/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipype) | `78.65% <100.00%> (-4.24%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipype#carryforward-flags-in-the-pull-request-comment) to find out more. | [Files Changed](https://app.codecov.io/gh/nipype/pydra/pull/689?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipype) | Coverage Δ | | |---|---|---| | [pydra/engine/workers.py](https://app.codecov.io/gh/nipype/pydra/pull/689?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipype#diff-cHlkcmEvZW5naW5lL3dvcmtlcnMucHk=) | `22.73% <100.00%> (+3.45%)` | :arrow_up: | ... and [16 files with indirect coverage changes](https://app.codecov.io/gh/nipype/pydra/pull/689/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nipype)

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[djarecka]

my changes were already merged to #686 so closing this