Bug#993214: mpi4py: autopkgtest regression around 2021-08-25

[Drew Parsons]

Source: mpi4py
Followup-For: Bug #993214

There have been some strange mpi failures. pytest-mpy also started
failing tests for no good reason.

spawning has been unreliable in OpenMPI for a long time, cf.
https://github.com/jsquyres/ompi/pull/4#issuecomment-806897758

mpi4py upstream informs me that OpenMPI 5 is fixing some substantial
problems, particularly with respect to spawning. Hopefully things will
be calmer in openmpi space once it's released.


The workaround is to skip spawning tests, done in 3.1.1 in experimental
mpi4py upstream is working to fix the s390x failure in mpi4py 3.1.1.

In the meantime I'll apply the workaround to unstable.