exclude mpi run from auto-detection of horovod

[awaelchli]

What does this PR do?

Fixes #8573

Horovod can be launched by either horovodrun (convenience utility) or by equivalent commands through mpirun directly (see docs). However, since mpirun is a general purpose HPC technology we probably don't want to autodetect horovod unless horovod is actually installed.

I'm very unfamiliar with the details of the mpirun + horovod usage, so suggestions are welcome.

Does your PR introduce any breaking changes? If yes, please list them.

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  • No, suggestions welcome. I tried to write a test but having trouble mocking the horovod imports pretending
    it is not installed. If you have any ideas, please let me know.
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[codecov]

Codecov Report

Merging #8610 (a1542b3) into master (c99e2fe) will decrease coverage by 4%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #8610    +/-   ##
=======================================
- Coverage      93%     88%    -4%     
=======================================
  Files         168     168            
  Lines       13951   13951            
=======================================
- Hits        12909   12315   -594     
- Misses       1042    1636   +594     

[tchaton]

Great catch !