make outlier testing deterministic

[chrisgorgo]

No description provided.

[codecov-io]

Codecov Report

Merging #1859 into master will increase coverage by 1.47%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1859      +/-   ##
==========================================
+ Coverage   73.04%   74.51%   +1.47%     
==========================================
  Files        1064     1065       +1     
  Lines       53366    62240    +8874     
==========================================
+ Hits        38980    46379    +7399     
- Misses      14386    15861    +1475

Flag	Coverage Δ
#unittests	74.51% <100%> (+1.47%)	⬆️

Impacted Files	Coverage Δ
nipype/algorithms/tests/test_confounds.py	95.34% <100%> (+0.11%)	⬆️
nipype/interfaces/dipy/setup.py	14.28% <0%> (-23.22%)	⬇️
...rfaces/slicer/tests/test_auto_SlicerCommandLine.py	87.5% <0%> (-12.5%)	⬇️
nipype/interfaces/camino/convert.py	61.88% <0%> (-9.94%)	⬇️
nipype/workflows/dmri/camino/group_connectivity.py	90.24% <0%> (-6.9%)	⬇️
nipype/interfaces/camino/odf.py	72.72% <0%> (-6%)	⬇️
nipype/interfaces/fsl/epi.py	66.21% <0%> (-4.24%)	⬇️
nipype/interfaces/afni/tests/test_auto_Merge.py	90% <0%> (-2.86%)	⬇️
...nterfaces/nipy/tests/test_auto_EstimateContrast.py	90.47% <0%> (-2.39%)	⬇️
nipype/interfaces/afni/preprocess.py	85.72% <0%> (-2.25%)	⬇️
... and 47 more

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[effigies]

Seems reasonable.