fix: propagate explicit workflow config to nodes in a workflow and allow nodes to overwrite

[satra]

Fixes # 2557.

Changes proposed in this pull request

• Simply set the node config to None on initialization
• This picks up the default when run is called.

@eort - please see if this branch solves your problem

[eort]

@satra Yes, that solves it.

[codecov-io]

Codecov Report

Merging #2559 into master will increase coverage by 0.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2559      +/-   ##
==========================================
+ Coverage   67.12%   67.14%   +0.01%     
==========================================
  Files         333      333              
  Lines       42538    42539       +1     
  Branches     5265     5265              
==========================================
+ Hits        28554    28563       +9     
+ Misses      13283    13274       -9     
- Partials      701      702       +1

Flag	Coverage Δ
#smoketests	50.71% <100%> (+0.03%)	⬆️
#unittests	64.49% <100%> (+0.03%)	⬆️

Impacted Files	Coverage Δ
nipype/pipeline/engine/nodes.py	84.29% <100%> (+0.35%)	⬆️
nipype/interfaces/base/specs.py	93.14% <0%> (-0.58%)	⬇️
nipype/pipeline/engine/utils.py	82.47% <0%> (+0.22%)	⬆️
nipype/utils/filemanip.py	78.3% <0%> (+0.23%)	⬆️
nipype/pipeline/plugins/multiproc.py	82.14% <0%> (+2.38%)	⬆️

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[effigies]

@satra Should this go in before the release?

[satra]

@effigies - it would be nice if it's not released yet, but i didn't want to hold back the release. i saw the pending PR for release.

[effigies]

My plan was to pass all tests today and push the button on Monday.