[MPI] MPICommunication should clone the communicator in the constructor.
As discussed in !1068 the MPICommunication class (https://gitlab.dune-project.org/core/dune-common/-/blob/master/dune/common/parallel/mpicommunication.hh#L110) in dune-common should in my opinion clonse (MPI_Comm_dup) the communicator passed in the constructor. Otherwise this can lead to some serious deadlock problems, for example, when using barriers etc or Send/Recv without tagging.