Fixes for tCompCor

[chrisgorgo]

• input mask is not being ignored anymore (fixes tCompCor ignores the input mask #1744)
• use np.percentile instead of implementing it by hand
• output the estimated high variance mask (useful for debugging)

[codecov-io]

Current coverage is 71.11% (diff: 68.42%)

Merging #1745 into master will decrease coverage by <.01%

@@             master      #1745   diff @@
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  Files          1028       1028          
  Lines         50608      50616     +8   
  Methods           0          0          
  Messages          0          0          
  Branches       7331       7333     +2   
==========================================
+ Hits          35992      35994     +2   
+ Misses        13491      13488     -3   
- Partials       1125       1134     +9   

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[djarecka]

did you change nipype/algorithms/tests/test_auto_TCompCor_test.py running python tools/checkspecs.py? I'm getting a different file when running python tools/checkspecs.py or make specs:
djarecka@ac65ea4