FIX: Python 2.7-3.7.1 compatible NonDaemonPool

[effigies]

Fixes #2745.

Python 2.7, 3.4-3.7.0, and 3.7.1 all have different interpretations of Pool.Process.

In Python 2.7, it's a class:

class Pool(object):
    '''
    Class which supports an async version of the `apply()` builtin
    '''
    Process = Process

In Python 3.4-3.7.0, it's a method that calls self._ctx.Process:

class Pool(object):
    '''
    Class which supports an async version of applying functions to arguments.
    '''
    _wrap_exception = True


    def Process(self, *args, **kwds):
        return self._ctx.Process(*args, **kwds)

And now, in Python 3.7.1, it's a static method that takes a context:

class Pool(object):
    '''
    Class which supports an async version of applying functions to arguments.
    '''
    _wrap_exception = True


    @staticmethod
    def Process(ctx, *args, **kwds):
        return ctx.Process(*args, **kwds)

[codecov-io]

Codecov Report

Merging #2754 into master will decrease coverage by 3.44%.
The diff coverage is 90.9%.

@@            Coverage Diff             @@
##           master    #2754      +/-   ##
==========================================
- Coverage   67.44%   63.99%   -3.45%     
==========================================
  Files         340      338       -2     
  Lines       43164    43116      -48     
  Branches     5351     5348       -3     
==========================================
- Hits        29110    27594    -1516     
- Misses      13355    14444    +1089     
- Partials      699     1078     +379

Flag	Coverage Δ
#smoketests	?
#unittests	63.99% <90.9%> (-0.81%)	⬇️

Impacted Files	Coverage Δ
nipype/pipeline/plugins/legacymultiproc.py	56.72% <90.9%> (+0.17%)	⬆️
nipype/interfaces/nilearn.py	40% <0%> (-56.67%)	⬇️
nipype/utils/spm_docs.py	25.92% <0%> (-44.45%)	⬇️
nipype/interfaces/freesurfer/base.py	49.59% <0%> (-30.9%)	⬇️
nipype/utils/logger.py	59.7% <0%> (-29.86%)	⬇️
nipype/algorithms/rapidart.py	35.39% <0%> (-29.21%)	⬇️
nipype/interfaces/spm/base.py	58.41% <0%> (-29.05%)	⬇️
nipype/utils/provenance.py	55.73% <0%> (-28.99%)	⬇️
nipype/interfaces/fsl/model.py	55.26% <0%> (-25.35%)	⬇️
nipype/interfaces/dipy/setup.py	0% <0%> (-25%)	⬇️
... and 47 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 39675df...c9a787e. Read the comment docs.

[effigies]

Relevant Travis tests: https://travis-ci.org/nipy/nipype/builds/446288741

@oesteban Any objections? I'm pretty sure the whole NonDaemonPool thing was something you needed, so want to make sure I'm not breaking anything subtly.

[oesteban]

Good job!

[Atterratio]

Awesome! @effigies Thanks a lot its help me in my own project!