Problem with OpenMPI 4 in Docker container

There are some security precautions enabled in the Docker container which keeps OpenMPI from doing it's job, see https://github.com/open-mpi/ompi/issues/4948. There are tons of errors/warnings produced looking like this

Read -1, expected <someNumber>, errno =1
Read -1, expected <someNumber>, errno =1
Read -1, expected <someNumber>, errno =1
...

I tried turning the offending mode of OMPI_MCA_btl_vader_single_copy_mechanism=none in the Docker (see https://git.iws.uni-stuttgart.de/timok/dumux-bb-ci/-/commit/3e5545ce7010f10219ebac9074faef207029df11) but the runtime seems to be affected a lot. The parallel test are much slower than the sequential tests. Another solution mentioned in https://github.com/open-mpi/ompi/issues/4948 requires to set some system permissions on the testing system. @root might be looking into that.

The issue started when I upgraded the Docker containers to use Ubuntu 20.04LTS. I did that to get the newer required CMake version as default (see !2136 (merged)). 20.04LTS also comes per default with a newer OpenMPI version (4.0.3 I think). That setup shows the problem described in https://github.com/open-mpi/ompi/issues/4948.