VTKHDFWriter not compatible with concurrent writing using MPI
When the VTKHDF Writer is called by several processes at the same time in an MPI setting, only the first process can write to the file, and the others raise an error.
Concurrent writing is supposed to work natively in HDF5. We should at least make sure that the writer is aware of MPI and that concurrent writing does not raise HDF5 errors, and then distribute the data evenly between processes for partitioned data.