Simplify working with containers and MPI

Currently, working in the recommended containers with MPI requires setting some environment variables. Since those are required for most use cases (i.e. testing parallel workloads), these should be configured by default.

The required environment variables are:

OMPI_ALLOW_RUN_AS_ROOT=1 and OMPI_ALLOW_RUN_AS_ROOT_CONFIRM=1 (for running MPI inside a container as root, see open-mpi.org)
OMPI_MCA_btl_vader_single_copy_mechanism=none (to avoid error messages like "Read -1, expected ..., errno =1", see github.com)

Edited Jun 16, 2022 by webmanue

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