[FIX]eddy command and multithreading

[mauriliogenovese]

I will send some PRs to improve/fix fsl cuda-capable tools with the new gpu support.
This one is about eddy:
eddy_openmp is an old command, new fls uses eddy_cpu
eddy_cuda is missing in some version, in those cases if user requests cuda, just use eddy

eddy_cpu does not enable multithread with OMP_NUM_THREADS variable but with --nthr argument

[codecov]

Codecov Report

Attention: Patch coverage is 44.44444% with 5 lines in your changes missing coverage. Please review.

Project coverage is 69.13%. Comparing base (2f85d92) to head (9348f49).

Files with missing lines	Patch %	Lines
nipype/interfaces/fsl/epi.py	44.44%	5 Missing ⚠️

Additional details and impacted files

@@ Coverage Diff @@ ## master #3721 +/- ## =========================================== + Coverage 2.88% 69.13% +66.24%  =========================================== Files 1279 1278 -1 Lines 59413 59271 -142 =========================================== + Hits 1717 40978 +39261  + Misses 57696 18293 -39403 

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[mauriliogenovese]

the second commit fix this:
EddyInputError: The version compiled for GPU can only use 1 CPU thread (i.e. --nthr=1)