ENH: Update MCFLIRT outputs for FSL 6+

[kimsin98]

Summary

Fixes #2925 .

List of changes proposed in this PR (pull-request)

• Fixes MCFLIRT output checks for FSL 6, which now uses more sensible extensions for intermediate output file names.

Acknowledgment

• (Mandatory) I acknowledge that this contribution will be available under the Apache 2 license.

[codecov]

Codecov Report

Merging #3029 into master will decrease coverage by 0.02%.
The diff coverage is 11.11%.

@@            Coverage Diff             @@
##           master    #3029      +/-   ##
==========================================
- Coverage    67.5%   67.48%   -0.03%     
==========================================
  Files         344      344              
  Lines       44062    44087      +25     
  Branches     5553     5561       +8     
==========================================
+ Hits        29746    29753       +7     
- Misses      13570    13587      +17     
- Partials      746      747       +1

Flag	Coverage Δ
#smoketests	50.28% <11.11%> (-0.01%)	⬇️
#unittests	64.94% <11.11%> (-0.03%)	⬇️

Impacted Files	Coverage Δ
nipype/interfaces/fsl/preprocess.py	82.04% <11.11%> (-0.56%)	⬇️
nipype/interfaces/afni/preprocess.py	80.91% <0%> (-1.07%)	⬇️

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[effigies]

Thanks!