OTF2: improve support for mpi communicators

This commit fix the problem that happens if the tracing tool that generates a trace did not use an MPI communicator.

added 3 commits

• a7db4a49...72b33654 - 2 commits from branch master
• c328d861 - Merge branch 'master' into otf2-communicator

Compare with previous version

Oups, there's something wrong with the CI configuration. It looks like the same problem as with the previous merge request, but applying the same changes in the CI configuration does not fix the problem :/

Yes it's weird. It worked out perfectly on the chameleon machine, but not on the other ones :(. I'll try to investigate that later.

Sorry for the delay, I totally forgot about it :(.

merged

mentioned in commit 5b8fe1fe