XML partitioned-dataset writer does not work in parallel correctly.

• Connect to pvserver (2 ranks) using ParaView
• Open can.ex2, apply
• Create Adaptive Resample to Image filter, Apply.
• Show as Surface and color by vtkProcessId to confirm there are as many blocks as ranks (2 in this case)
• Save data as foo.vtpd

Now restart ParaView (as builtin) and load the file that was saved. Either it will fail to load correctly or will only have 1 block. This is a bug.

This is happening because the writer for vtkPartitionedDataSet is not parallel aware and each rank ends up overwriting what an other rank wrote.

Same is probably true for vtkPartitionedDataSetCollection.