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.
[A venir] Mise en place de quotas sur nos instances GitLab. Plus d'information sur : https://doc-si.inria.fr/pages/viewpage.action?pageId=129728565
[Coming soon] Quotas installation on our GitLab instances. More information: https://doc-si.inria.fr/pages/viewpage.action?pageId=129728565
This commit fix the problem that happens if the tracing tool that generates a trace did not use an MPI communicator.